Add note that block-box is not supported
Add note that block-box is not supported

The block-box files were added to show a proof of concept for running
Cinder as a containerized service and has not been maintained. Some of
the files may still be useful for someone that is looking for some
pointers on how to do this, but there are other projects now that are
focused on containerizing OpenStack services.

This adds a note to the README to make it clear it is not supported.

Closes-bug: #1859158

Change-Id: I36c23cc0f61d67e70fe6302c2d0d2501959b28fc
Signed-off-by: Sean McGinnis <961eeb09b6d45516665e15b82e013282c4faf575@gmail.com>

openstack/cinder,openstack/cinder,mahak/cinder,mahak/cinder