maint policy: Move paragraph about controversial changes

maint policy: Move paragraph about controversial changes

The point was also raised during discussions over whether to include
perlunicook.pod in 5.20.2 that exceptions can be made to the rules under
the terms of "Rule 2" and the fact that the pumpking is acting on Larry's
behalf. However, this is probably best left being implicit, rather than
explicitly stating it. Exceptions should be exceptional; we don't want to
encourage them!