Improve documentation

[gadamc]

Setup auto documentation creation with sphinx: https://www.sphinx-doc.org/en/master/

[gadamc]

Open to alternative ways to generate documentation, however. Sphinx requires writing in resturcturedTxt format, which is just one more thing to learn. Consider pdoc or pydoc. Ideally, would be able to publish on readthedocs, but that's probably not necessary as long as there's a way to render the output.