docs: add code review scenario to sharing guide The idea is to demonstrate a simpler multiple-developer situation that does not involve getting into trouble. The final scenario illustrates Alice and Bob getting into trouble with bumped and divergent changesets by amending each other's history. The required tests and text are all written, but will need to be heavily revised because of the inserted scenario.

test-drop.t
test-simple4server.t
tests/test-simple4server-bundle2.t