Automate docs deployment for simoc

[ezio-melotti]

The documentation is currently hosted at https://simoc.space/docs/user_guide/ but it's not automatically updated.
In order to update it automatically we should:

• update the docs/conf.py file so that there are no warnings/errors
  • Fix incorrect rst markup and tweak conf.py. #211
• add a build-docs command to simoc.py
• add a workflow that builds the docs and uploads them to simoc.space
  • Add a workflow to build/check/upload docs. #212