docs: update appendix

[Gaiejj]

Description

Move the appendix from our paper to website docs.

Types of changes

What types of changes does your code introduce? Put an x in all the boxes that apply:

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds core functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [x] Documentation (update in the documentation)

Checklist

Go over all the following points, and put an x in all the boxes that apply. If you are unsure about any of these, don't hesitate to ask. We are here to help!

• [x] I have read the CONTRIBUTION guide. (required)
• [x] My change requires a change to the documentation.
• [ ] I have updated the tests accordingly. (required for a bug fix or a new feature)
• [x] I have updated the documentation accordingly.
• [x] I have reformatted the code using make format. (required)
• [x] I have checked the code using make lint. (required)
• [x] I have ensured make test pass. (required)

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

Project coverage is 96.96%. Comparing base (080e6b8) to head (ef5e25f). Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
omnisafe/envs/safety_gymnasium_modelbased.py	75.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #350 +/- ## ========================================== - Coverage 97.03% 96.96% -0.08% ========================================== Files 137 136 -1 Lines 6906 6768 -138 ========================================== - Hits 6701 6562 -139 - Misses 205 206 +1 ```

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