Add cookbook for 2d annulus pyvista visualization

[KerrMadeleine]

I have made a short cookbook that describes how to use the pyvista 2D annulus visualization script [aspect/contrib/python/scripts/pyvista_2d_annulus_example.py]. The parameter file used to make the models that I ran the script on is in the cookbook directory. The output figures (angular, radial velocity and temperature deviation) and a document describing how the script works are also available in the doc/ sub-directory.

[cedrict]

I have no more comments.

[gassmoeller]

/rebuild