Motivation
For better or for worse, sphinx is still a very popular documentation engine and I foresee some users still wanting to use it (rather than mkdocs (#188) which is what would be used as a part of the higher level interface (#298)). At my workplace, we currently use it.

It doesn't make sense to do this until #188 is complete and the mkdocs workflow is a bit more mature - there's probably quite a few integrations and cute options that we'd want to support (e.g. a CLI option for setting the logo?) which make sense to get right in mkdocs before moving to sphinx. There's also the question of how to test it, which needs to be resolved.

Summary of desired enhancement
Create a way to add sphinx documentation to a project.