Docs: Improve mixed model documentation #2078
Description
We already have some documentation on the use of mixed models, but i can be improved.
e.g.
- What are the semantics of
@Pinnedand@PinnedtoIndexwhen using a mixed model? - How are these variables initialized? (I am seeing 2 construction heuristic phases)
- What pitfalls are there? (need more nudging of custom moves to not only change just 1 variable?)
- ....