R1:2823547f2c70

Update contributor documentation

Summary:
It's fairly common for people to show up and be interested in finding easy stuff to work on. This stuff basically doesn't exist and probably never will: it doesn't make much sense to deliberately leave easy bugs broken just because someone might show up and want to fix a couple of easy bugs.

Almost all of the work that's valuable to us requires a depth or bredth of context which can't be acquired in a few hours here and there, and probably always will. I think it…