docs: set up readthedocs

[aluu317]

This PR includes Sphinx to set up docs configuration. I'd like to host the docs on readthedocs site so it's publicly available.

Setup instructions https://docs.readthedocs.io/en/stable/tutorial/index.html

Based on an example of readthedocs of caikit project: https://caikit.readthedocs.io/en/latest/index.html