Add missing docstrings to settings.rs (#9054)

![image](https://github.com/zed-industries/zed/assets/1290639/46c13110-8506-4b03-91d4-b1cfcafe824a)

Add documentation for theme-related settings.

Release Notes:

- Add documentation for theme-related settings ([8383](https://github.com/zed-industries/zed/issues/8383))
6a7a3b257aJadi committed on 3/8/2024, 10:46:47 PM· committed by GitHubparent8a6264d
1 file changedLine totals unavailable