Feature: Add sphinx docs deployed to gitlab pages

Hi there! Here is a minimal sphinx documentation that gets automatically deployed to the gitlab pages of this project! Please check out if you're happy with it. For the getting started guide, I mostly just copied the cookbook. I also added some doctests that we could run during the unit testing stage.

(Side note: I think it's crucial to write some unit tests for this package...)

Resolves #2 (closed)