Explicitly require a Use Cases section for Kilo

We should put more stress on making it easy to figure out what the use
case is for every blueprint.  All blueprints should have a use case for
someone.

Related to: I7075a130c01be22f3ee5315d4a65b8e524b5a1ad

Change-Id: I7f378054b52488e6347304d3894868caa234b4fd