Updates Jax doc to overwrite version < 0.6.0 for torch (#572)

# Description

Jax >= 0.6.0 is incompatible with torch 2.7, but is installed by default
when running pip install skrl[jax]. We update the installation
instructions to override the version of jax to be < 0.6.0 after
installing skrl dependencies to avoid the version incompatibilities.


## Type of change

- This change requires a documentation update

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.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
- [ ] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

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docs/source/overview/reinforcement-learning/rl_existing_scripts.rst

@@ -149,6 +149,8 @@ SKRL
             ./isaaclab.sh -i skrl
             # install skrl dependencies for JAX
             ./isaaclab.sh -p -m pip install skrl["jax"]
+            # install jax<0.6.0 for torch 2.7
+            ./isaaclab.sh -p -m pip install "jax[cuda12]<0.6.0"
             # run script for training
             ./isaaclab.sh -p scripts/reinforcement_learning/skrl/train.py --task Isaac-Reach-Franka-v0 --headless --ml_framework jax
             # run script for playing with 32 environments