These sites are good places to learn about Read the Docs (RtD), Sphinx, and all the things you can do in .rst files:
RtD dashboard (you must be logged in)
RtD documentation (in other words, RtD’s RtD site)
To write more effective software documentation generally, here are some useful sites:
The 18F Content Guide houses best practices for software documentation focused on user experiences and needs, particularly as related to government websites.
Write the Docs, a community focused on communication and documentation, has a catalog of learning resources (including videos and tutorials) as well as a robust documentation guide. This community also has a GitHub repo.
Docs as Code provides resources for development teams to build documentation repeatably and consistently across multiple platforms.
The Documentation System emphasizes four types of documentation: tutorials, how-to guides, technical reference, and explanation documents. The site provides examples of and tips for each.
The Good Docs Project, to which you can contribute, includes templates and writing instructions for documenting open source software. The organization’s templates go through a rigorous writing, reviewing, and refining process.
The Beautiful Docs repo has a list of language- and program-specific documentation resources.