Update README with link to Blueprint wiki

Add a link so people can find the current blueprint process. This
ways its more obvious that we still use launchpad to track
blueprints.

At the same time, remove the Milestones section from the template,
to ensure all tracking is in launchpad.

Change-Id: I1ef3d0d010deddae4eb398e801810137276ebffb
Add a note to be clear about actors in use cases

There has been much confusion on the End User and Deployer view
when reviewing some blueprints. I have added a note to be clear
on the distinctions between these two main groups.

This idea was take from and early revision of:
https://review.openstack.org/#/c/82166

Change-Id: Id56330df05d8461b821ef124361299bc1d5ec3fb
Merge "Add a note to be clear about actors in use cases"