Show an example of solver rejection in docs

[philderbeast]

          > The documentation doesn't have any example of solver rejection?

Searching for "rejecting" in *.rst gets no hits.

Originally posted by @philderbeast in #9824 (comment) in response to a question posed by @Kleidukos.

I remember when first trying out cabal, seeing the solver rejection message and not being able to come up with a solvable set of versions. It would be nice to have some walk-throughs on how to deal with these with examples.