WIP: [doxygen] Add doc for grid geometry.
What this MR does / why does DuMux need it:
This MR adds a first try for a documentation on the gridgeometry
.
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:
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does the new code follow the style guide? -
do the test pipelines pass? (see guide on how to run pipelines for a merge request)