DOC: Incorporate/revise cookbook.rst

[larsoner]

For @drammock at some point, from #6767 and for 0.20. cookbook.rst is a bit outdated. Maybe it can even just be replaced by a table of contents linking to other PRs (maybe after making the set of tutorials more complete)...?

[larsoner]

@drammock I'm going to push the milestone on this to 0.21, but if you feel like it's doable in the next two weeks feel free to set back to 0.20

[britta-wstnr]

We talked about this in the office hours today - let's see if we can get this done now.

[larsoner]

Just to add that we should incorporate ideas from #3669 when working on this