add 'project' notifications to docs

In addition to adding a mention about 'project' notifications, I rewrote
a few bits of the notifications docs to make it easier to add new
resource types as we implement them (you only have to add them to the
list, rather than revising a bunch of disparate paragraphs).

blueprint notifications

Change-Id: I4792e5dd368d5404c252d6c7c8dc8813af7509d8
Merge "add 'project' notifications to docs"