Context

https://github.com/executablebooks/sphinx-book-theme/blob/master/CONTRIBUTING.md
points to
https://github.com/executablebooks/sphinx-book-theme/blob/master/docs/contributing/index.md

Proposal

Instead, I think it would be better to point to:
https://sphinx-book-theme.readthedocs.io/en/stable/contributing/index.html

Tasks and updates

No response