This updates the Bug Life Cycle docs now that we've switched to GitHub
issues. The intent is to retain the same general process we used to
use for triaging bugs under Bugzilla, but with the facilities we have
available in GitHub.
Document what is expected during:
* triaging
* actively working on a bug
* closing/resolving
Also document how we maintain:
* product/component breakdown
* default-cc lists per component
Differential Revision: https://reviews.llvm.org/D53691
llvm-svn: 346299