Add documentation

[RBerga06]

Is your feature request related to a problem? Please describe. This is a Python library, and it might be useful to add documentation to it.

Describe the solution you'd like Add documentation. This will also enable us to run doctest in the future.

Describe alternatives you've considered N/A

Additional context N/A

[RBerga06]

We're going to use sphinx to build our documentation. We should choose a docstring format. I think we'll go with ReStructuredText (see PEP 287).

[RBerga06]

GitHub Actions are not properly configured