NGEE Tutorial setup documentation (aka user's guide)

[glemieux]

This is documentation to be hosted only via read the docs to provide an easily accessible format to guide tutorial attendees through the setup process. The documentation content is currently hosted at the https://github.com/NGEET/tutorial-containers/tree/main/docs. This is distinct from the tutorial content itself which is hosted on https://github.com/NGEET/fates-tutorial and accessed via containerized jupyter notebooks.

### Tasks
- [x] Create a development branch
- [x] Update readthedocs to build pull requests

[glemieux]

The setup documentation is complete. That said the lesson content still needs updating.