Generate proper documentation

README.md has grown to 200 lines, and spans error codes, installation & run instructions, configuration and command-line flags. We also have CHANGELOG.md with 150 lines.
There are a few links in the readme, but it would probably be quite useful to have anything referring to [objects within] urllib3, httpx, anyio, asyncio, trio, etc be hyperlinks w/o having to manually update.
Pulling out the error messages for the documentation automatically would be nice, but somewhat complicated given the current setup for messages differing for different (combinations of) libraries. Should be quite doable though.

https://github.com/python-trio/flake8-async/issues/211#issuecomment-1971778351

I'm planning to write up some more detail about each of our error codes in a long doc, hopefully this weekend, which will include much more about why you'd want to enable each of the optional rules in addition to the existing material.

This also sounds like great doc material.

The one workflow I'm decently accustomed to is ReadTheDocs+Sphinx as used in python-trio/trio, and probably nice to be consistent with it since it's in the same organization. But it's also been a huge pain to work with at times.

Start by reviewing README.md and CHANGELOG.md, then compare the project's current documentation setup with the mentioned ReadTheDocs and Sphinx workflow used by Trio. Define the documentation structure, hyperlinking approach, and treatment of error messages before making changes; done means the project information and error-code guidance are organized and generated links or content stay maintainable.