Add docs for case_validate - #104

@kchason : PR 99 had updated the develop branch to work with Python 3.8, in its setup.cfg and its CI script. Your PR against main fails CI because a pre-commit module now requires Python 3.8. PR 99 had made the bump to 3.8 because of another dependency.

Could you please re-do this PR, cherry-picking f97aad8 to be based off of develop instead of main, and either re-point this PR to develop or make a new PR against develop?

@kchason , very sorry, I didn't look at the actual change, I just diagnosed the CI failure instead.

None of the tools provided by this repository currently have their --help menus dumped into the README.

I've known some other repositories to do this, but without scripting support. This induced some documentation drift, because there wasn't a build system for the README.

case_validate would need to have its README section regenerated with just about every case-utils release - at least, the ones that include a new ontology build.

I'm more inclined to NACK this PR without scripting, because it would add person-time to rebuilding the README. We can script this; every data-driven example across CASE currently uses an Autotools-style sed pipeline (see e.g. the @'s in the Owl Trafficking index source, processed with this recipe). However, I'm not quite sure how to constrain the "page width" (terminal width); it looks like we'd use RawTextHelpFormatter (via this StackOverflow answer)?

In the end - if you'd like the --help menus to be visible, I would like to not have to re-build them myself, but I'm fine with them being scripted. Are the generated --help menus something we should provide?