Puts the AppLauncher tutorial later in the series (#341)

# Description

Currently, the very first tutorial for users is the app launcher. This
might be a bit overwhelming to start with. This MR iterates over the app
launcher tutorial and puts it later in the part 1 of the tutorials.

## Type of change

- This change requires a documentation update

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./orbit.sh --format`
- [x] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [x] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

docs/source/tutorials/00_sim/index.rst

@@ -9,6 +9,6 @@ simulated scene. They cover the following APIs: :class:`~omni.isaac.orbit.app.Ap
     :maxdepth: 1
     :titlesonly:
 
-    launch_app
     create_empty
     spawn_prims
+    launch_app

docs/source/tutorials/00_sim/launch_app.rst

-Launching Isaac Sim from AppLauncher
-====================================
+Deep-dive into AppLauncher
+==========================
 
 .. currentmodule:: omni.isaac.orbit
 
 In this tutorial, we will dive into the :class:`app.AppLauncher` class to configure the simulator using
-CLI arguments and environment variables (envars). Particularly, we will demonstrate how to use :class:`~app.AppLauncher`
-to enable livestreaming and configure the :class:`omni.isaac.kit.SimulationApp` instance it wraps,
-while also allowing user-provided options.
+CLI arguments and environment variables (envars). Particularly, we will demonstrate how to use
+:class:`~app.AppLauncher` to enable livestreaming and configure the :class:`omni.isaac.kit.SimulationApp`
+instance it wraps, while also allowing user-provided options.
 
-Motivation
-----------
-
-The :class:`~app.AppLauncher` is a wrapper for :class:`~omni.isaac.kit.SimulationApp` to simplify its configuration.
-The :class:`~omni.isaac.kit.SimulationApp` has many extensions that must be loaded to enable different capabilities, and some of these extensions are order- and inter-dependent.
-Additionally, there are startup options such as ``headless`` which must be set at instantiation time, and which have an implied relationship with
-some extensions, e.g. the livestreaming extensions. The :class:`~app.AppLauncher` presents an interface that can handle these extensions and startup options
-in a portable manner across a variety of use cases. To achieve this, we offer CLI and envar flags which can be merged with user-defined CLI args,
-while passing forward arguments intended for :class:`~omni.isaac.kit.SimulationApp`.
+The :class:`~app.AppLauncher` is a wrapper for :class:`~omni.isaac.kit.SimulationApp` to simplify
+its configuration. The :class:`~omni.isaac.kit.SimulationApp` has many extensions that must be
+loaded to enable different capabilities, and some of these extensions are order- and inter-dependent.
+Additionally, there are startup options such as ``headless`` which must be set at instantiation time,
+and which have an implied relationship with some extensions, e.g. the livestreaming extensions.
+The :class:`~app.AppLauncher` presents an interface that can handle these extensions and startup
+options in a portable manner across a variety of use cases. To achieve this, we offer CLI and envar
+flags which can be merged with user-defined CLI args, while passing forward arguments intended
+for :class:`~omni.isaac.kit.SimulationApp`.
 
 
 The Code
-~~~~~~~~
+--------
 
-The tutorial corresponds to the ``launch_app.py`` script in the ``orbit/source/standalone/tutorials/00_sim`` directory.
+The tutorial corresponds to the ``launch_app.py`` script in the
+``orbit/source/standalone/tutorials/00_sim`` directory.
 
 .. dropdown:: Code for launch_app.py
    :icon: code
 
    .. literalinclude:: ../../../../source/standalone/tutorials/00_sim/launch_app.py
       :language: python
-      :emphasize-lines: 17-41
+      :emphasize-lines: 18-40
       :linenos:
 
 The Code Explained
-~~~~~~~~~~~~~~~~~~
+------------------
+
+Adding arguments to the argparser
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+:class:`~app.AppLauncher` is designed to be compatible with custom CLI args that users need for
+their own scripts, while still providing a portable CLI interface.
 
-:class:`~app.AppLauncher` is designed to be compatible with custom CLI args that users need for their own scripts,
-while still providing a portable CLI interface. In this tutorial, a standard :class:`argparse.ArgumentParser` is instantiated
-and given the script-specific ``--size`` argument, as well as the arguments ``--height`` and ``--width``. The latter
-are ingested by :class:`~omni.isaac.kit.SimulationApp`.
+In this tutorial, a standard :class:`argparse.ArgumentParser` is instantiated and given the
+script-specific ``--size`` argument, as well as the arguments ``--height`` and ``--width``.
+The latter are ingested by :class:`~omni.isaac.kit.SimulationApp`.
 
-The argument ``--size`` is not used by :class:`~app.AppLauncher`, but will merge seamlessly with the :class:`~app.AppLauncher`
-interface. In-script arguments can be merged with the :class:`~app.AppLauncher` interface via the :meth:`~app.AppLauncher.add_app_launcher_args` method,
-which will return a modified :class:`~argparse.ArgumentParser` with the :class:`~app.AppLauncher` arguments appended. This can then be processed
-into an :class:`argparse.Namespace` using the standard :meth:`argparse.ArgumentParser.parse_args` method and passed directly to :class:`~app.AppLauncher` for instantiation.
-This illustrates only one of several ways of passing arguments to :class:`~app.AppLauncher`, please consult its documentation page to see further options.
+The argument ``--size`` is not used by :class:`~app.AppLauncher`, but will merge seamlessly
+with the :class:`~app.AppLauncher` interface. In-script arguments can be merged with the
+:class:`~app.AppLauncher` interface via the :meth:`~app.AppLauncher.add_app_launcher_args` method,
+which will return a modified :class:`~argparse.ArgumentParser` with the :class:`~app.AppLauncher`
+arguments appended. This can then be processed into an :class:`argparse.Namespace` using the
+standard :meth:`argparse.ArgumentParser.parse_args` method and passed directly to
+:class:`~app.AppLauncher` for instantiation.
 
 .. literalinclude::  ../../../../source/standalone/tutorials/00_sim/launch_app.py
    :language: python
    :start-at: import argparse
    :end-at: simulation_app = app_launcher.app
 
-To illustrate this process, we can pass the ``--help`` argument and see the combined outputs of our custom arguments and
-those from :class:`~app.AppLauncher`.
+The above only illustrates only one of several ways of passing arguments to :class:`~app.AppLauncher`.
+Please consult its documentation page to see further options.
+
+Understanding the output of --help
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+While executing the script, we can pass the ``--help`` argument and see the combined outputs of the
+custom arguments and those from :class:`~app.AppLauncher`.
 
 .. code-block:: console
 
@@ -79,27 +93,38 @@ those from :class:`~app.AppLauncher`.
    --ros {0,1,2}         Enable ROS middleware. Mapping corresponds to that for the "ROS_ENABLED" environment variable
    --offscreen_render    Enable offscreen rendering when running without a GUI.
 
-This readout details the ``--size``, ``--height``, and ``--width`` arguments defined in the script directly, as well as the :class:`~app.AppLauncher` arguments.
-An ``[INFO]`` message preceding the help output also reads out which of these arguments are going to be interpreted as arguments to the :class:`~omni.isaac.kit.SimulationApp` instance which :class:`~app.AppLauncher` wraps,
-in this instance ``--height`` and ``--width``. These are classified as such because they match the name and type of an argument which can be processed by :class:`~omni.isaac.kit.SimulationApp`.
-Please refer to the `specification`_ for such arguments for more examples.
-As noted in the help message, the :class:`~app.AppLauncher` arguments correspond to the envars described in :mod:`omni.isaac.orbit.app`. Providing any of these arguments is equivalent to
-running the script in a shell environment where the corresponding envar is set- :class:`~app.AppLauncher` envars are simply a convenience to provide session-persistent configurations,
-and can be set in the user's ``.bashrc`` for persistent settings between sessions. In the case where these arguments are provided, they will override their corresponding envar, as we
-will demonstrate below.
+This readout details the ``--size``, ``--height``, and ``--width`` arguments defined in the script directly,
+as well as the :class:`~app.AppLauncher` arguments.
 
-These arguments can be used with any script that starts the simulation using :class:`~app.AppLauncher`, with one exception, ``--offscreen_render``.
-The :class:`omni.isaac.orbit.sim.SimulationContext`  class controls many aspects of simulation execution, including the rendering pipeline. This makes it required when we
-want to use the ``--offscreen_render`` argument, because ``--offscreen_render`` pipeline depends on behavior within :class:`~omni.isaac.orbit.sim.SimulationContext`.
-For more information on the ``--offscreen_render`` flag, please see the :class:`~app.AppLauncher` API doc.
+The ``[INFO]`` messages preceding the help output also reads out which of these arguments are going
+to be interpreted as arguments to the :class:`~omni.isaac.kit.SimulationApp` instance which the
+:class:`~app.AppLauncher` class wraps. In this case, it is ``--height`` and ``--width``. These
+are classified as such because they match the name and type of an argument which can be processed
+by :class:`~omni.isaac.kit.SimulationApp`. Please refer to the `specification`_ for such arguments
+for more examples.
+
+Using environment variables
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+As noted in the help message, the :class:`~app.AppLauncher` arguments (``--livestream``, ``--ros``)
+have corresponding environment variables (envar) as well. These are detailed in :mod:`omni.isaac.orbit.app`
+documentation. Providing any of these arguments through CLI is equivalent to running the script in a shell
+environment where the corresponding envar is set.
+
+The support for :class:`~app.AppLauncher` envars are simply a convenience to provide session-persistent
+configurations, and can be set in the user's ``${HOME}/.bashrc`` for persistent settings between sessions.
+In the case where these arguments are provided from the CLI, they will override their corresponding envar,
+as we will demonstrate later in this tutorial.
+
+These arguments can be used with any script that starts the simulation using :class:`~app.AppLauncher`,
+with one exception, ``--offscreen_render``. This setting is sets the rendering pipeline to use the
+offscreen renderer. However, this setting is only compatible with the :class:`omni.isaac.orbit.sim.SimulationContext`.
+It will not work with Isaac Sim's :class:`omni.isaac.core.simulation_context.SimulationContext` class.
+For more information on this flag, please see the :class:`~app.AppLauncher` API documentation.
 
-.. literalinclude::  ../../../../source/standalone/tutorials/00_sim/launch_app.py
-   :language: python
-   :start-at: def main():
-   :end-at: sim = sim_utils.SimulationContext(sim_cfg)
 
 The Code Execution
-~~~~~~~~~~~~~~~~~~
+------------------
 
 We will now run the example script:
 
@@ -108,11 +133,12 @@ We will now run the example script:
    LIVESTREAM=1 ./orbit.sh -p source/standalone/tutorials/00_sim/launch_app.py --size 0.5
 
 This will spawn a 0.5m\ :sup:`3` volume cuboid in the simulation. No GUI will appear, equivalent
-to if we had passed the ``--headless`` flag because headlessness is implied by our ``LIVESTREAM`` envar. If a
-visualization is desired, we could get one via Isaac's `Native Livestreaming`_. The process can be killed by pressing ``Ctrl+C`` in the launching terminal.
+to if we had passed the ``--headless`` flag because headlessness is implied by our ``LIVESTREAM``
+envar. If a visualization is desired, we could get one via Isaac's `Native Livestreaming`_. The
+process can be killed by pressing ``Ctrl+C`` in the launching terminal.
 
 
-Now we will look at how :class:`~app.AppLauncher` handles conflicting commands:
+Now, let's look at how :class:`~app.AppLauncher` handles conflicting commands:
 
 .. code-block:: console
 
@@ -123,7 +149,8 @@ This will cause the same behavior as in the previous run, because although we ha
 in our envars, CLI args such as ``--livestream`` take precedence in determining behavior. The process can
 be killed by pressing ``Ctrl+C`` in the launching terminal.
 
-Finally, we will examine passing arguments to :class:`~omni.isaac.kit.SimulationApp` through :class:`~app.AppLauncher`:
+Finally, we will examine passing arguments to :class:`~omni.isaac.kit.SimulationApp` through
+:class:`~app.AppLauncher`:
 
 .. code-block:: console
 
@@ -132,7 +159,9 @@ Finally, we will examine passing arguments to :class:`~omni.isaac.kit.Simulation
 
 This will cause the same behavior as before, but now the viewport will be rendered at 1920x1080p resolution.
 This can be useful when we want to gather high-resolution video, or we can specify a lower resolution if we
-want our simulation to be more performant. The process can be killed by pressing ``Ctrl+C`` in the launching terminal.
+want our simulation to be more performant. The process can be killed by pressing ``Ctrl+C`` in the launching
+terminal.
+
 
 .. _specification: https://docs.omniverse.nvidia.com/py/isaacsim/source/extensions/omni.isaac.kit/docs/index.html#omni.isaac.kit.SimulationApp.DEFAULT_LAUNCHER_CONFIG
 .. _Native Livestreaming: https://docs.omniverse.nvidia.com/isaacsim/latest/installation/manual_livestream_clients.html#omniverse-streaming-client