Add GitHub action step for doc generation and deployment

Upon a merge into master (after successful testing and review), we can trigger building the docs with sphinx and uploading to readthedocs.

Thoughts:

• add a check to see if the doc sources have changed so we don't deploy if everything's the same
• consider using https://github.com/readthedocs/actions for doc preview in a PR
• add a linting check for code documentation (e.g. https://docs.astral.sh/ruff/rules/#pydocstyle-d)

[rjplevin]

It's not just changes in doc sources that matter: the API documentation is driven by the code & comments therein. I would just rebuild the docs each time.

Seems fine to me—no need to preemptively optimize 😃

I also found this resource on connecting github accounts and on manual integrations.