Add docs build and update descriptons

[ml-evs]

This PR adds a mkdocs-based build of the documentation, to be served alongside the app.

• README updates: changing links and style, as well as some wording
• Docstring updates to code to better support docs (including LaTeX equations: somehow puts the emphasis on the rendered docs over the docstrings but I think its nice for this case).
• CI build of docs that should get deployed at least to the test server for now. Probably be available from {TEST_URL}/site/index.html initially, but we can move things around to be something more sensible. Not sure what Azure actually exposes yet

Some screenshots of the built docs: