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.
A few things to note: we have not yet created the confirmed label, but that is expected to be done shortly. There is already label confusion involving whether we should use beginner (89 issues) or good first issue (29 issues), so I went with good first issue in the documentation due to review feedback. I think we should strongly discourage users from creating arbitrary labels on their own because the labels will become useless pretty quickly if there's no consistency as to which are used, so I adjusted the docs accordingly.