More explanations and visualisations are needed

[lauraporta]

Is your feature request related to a problem? Please describe.

1. Rotation + Derotation is very confusing to people
   Now that I am introducing the Rotator class, it is harder to keep in mind how it works in comparison to the derotation. I also get confused when explaining it to people.
2. The interplay of incremental and full rotation is also very confusing.
3. It's not clear how to re-create the images used in regression tests.

Describe the solution you'd like
Text:

• longer docstrings, blocks of descriptions at the top of the files.
• Expand the content of the readme:
  • describe how exactly all the modules work
  • move the content to documentation (docs folder)

Animations:

• in the documentation, include plots and animations.