Add docs

[dwhswenson]

Sphinx-based documentation.

There's certainly more content to add in the docs, but this will at least put in the framework (and a lot of the most important content).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.29%. Comparing base (604af81) to head (bf40fa8).
Report is 9 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #10   +/-   ##
=======================================
  Coverage   99.29%   99.29%           
=======================================
  Files          15       15           
  Lines         853      853           
=======================================
  Hits          847      847           
  Misses          6        6           

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[Copilot]

Copilot reviewed 6 out of 17 changed files in this pull request and generated 1 comment.

Files not reviewed (11)

• docs/Makefile: Language not supported
• docs/cli.rst: Language not supported
• docs/index.rst: Language not supported
• docs/make.bat: Language not supported
• docs/reference/cli.rst: Language not supported
• docs/reference/filters.rst: Language not supported
• docs/reference/index.rst: Language not supported
• docs/reference/main.rst: Language not supported
• docs/reference/output.rst: Language not supported
• docs/reference/sources.rst: Language not supported
• docs/reference/utils.rst: Language not supported

[dwhswenson]

I don't think RTD will actually build until we've got the .readthedocs.yaml file on the main branch. But I have, in principle, set up RTD for this repo. I'd debug any RTD-specific build issues (and set up the RTD build as a check on a PR) after this gets merged.