What this MR does / why does DuMux need it:
This MR adds a first try for a documentation on the
Notes for the reviewer
Follow the instructions on https://dumux.org/docs/doxygen/master/building-the-documentation.html to build the documentation locally. The added description can be found under "Module documentation -> Discretization schemes".
Before you request a review from someone, make sure to revise the following points: