Ground plane tutorial correction

[louislelay]

Description

To verify the proper installation of IsaacLab, a test is performed using the script source/standalone/tutorials/00_sim/create_empty.py. As mentioned in issue #1265, the tutorial suggests that a black plane should appear, but none was initialized in the script, which could be misleading. Without the black plane, users might assume there is an error. To address this, I updated the script to ensure the ground plane is displayed.

Fixes #1265

Type of change

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

Screenshots

Before	After

Checklist

• I have run the pre-commit checks with ./isaaclab.sh --format
• I have made corresponding changes to the documentation
• 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

[louislelay]

While following the tutorials, I noticed that in the tutorial for creating an empty scene, the create_empty.py script also mentioned here was not supposed to generate a ground. So, rather than modifying this script to add a ground, it might be better to create a separate script to verify the installation.