Summary:
Most of our internal extensions don't have any docstringa causing hg help
to show nothing. I think this is confusing, as we teach people to use hg help.
In particular for our extensions they won't find anything on the internet
but hg help won't help either. So let's add rudimentary help texts.
Also ensure that gitnode is properly documented in hg help revset.
Test Plan:
added extensions, checked hg help and hg help extension. Also
checked hg help revset for gitnode.
Reviewers: rmcelroy, durham, sid0, akushner
Differential Revision: https://phabricator.fb.com/D1645964
A change in core mercurial added --edit to the commit options. This conflicted
with the fbamend --edit, which caused hg commit --amend -l foo.txt to actually
open the editor. Breaking arc diff.