Fixes image link in documentation (#2066)

# Description

Fixes image link in documentation, the previous image was not added to
the repo by accident

## Type of change

- Bug fix (non-breaking change which fixes an issue)

## Screenshots

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## 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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Author: kellyguo11