Add mission statement to Cinder

At the TC meeting on 2014-03-25 we did a gap
analysis on the Cinder project and identified that
Cinder still doesn't have an official mission statement.

This change adds the Cinder mission statement and matches
that which is included on the Cinder Wiki page.

Change-Id: I38753f778663bbd22418581ab752efc6f90da29d
Merge "Add mission statement to Cinder"