Adds Internal template generator warning for case when user pip installed isaaclab (#3027)

# Description

User may install isaaclab with pip but also want to create an internal
template in cloned isaaclab that doesn't sit in miniconda's python
site-packages, and of course this internal template will not be detect
by python, but we also don't want to create templates in site-package
neither, nobody do development in site-packages

The proper fix is to support both internal and external template
regardless the method user pick to install isaaclab, but for now, we
will add the warning to documentation that internal template with pip
isaaclab package is not supported


Fixes # (issue)

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## Type of change

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- Bug fix (non-breaking change which fixes an issue)
- This change requires a documentation update

## Screenshots

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## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [ ] 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

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docs/source/overview/developer-guide/template.rst

@@ -22,6 +22,12 @@ The template generator enables you to create an:
 * **Internal task**: A task that is part of the Isaac Lab repository. This approach should only be used to create
   new tasks within the Isaac Lab repository in order to contribute to it.
 
+  .. warning::
+
+    If you installed Isaac Lab via pip, any task generated by template outside of the pip-installed environment may not
+    be discovered properly. We are working on better support, but please prefer external projects when using
+    isaac lab pip installation.
+
 Running the template generator
 ------------------------------