API doc for Inherited Role Assignments to Projects

Changes regarding the functionality of Inherited Roles Assignments
to Projects.

Co-Authored-By: Raildo Mascena <raildo@lsd.ufcg.edu.br>
Depends On: blueprint hierarchical-multitenancy

Change-Id: I6985d5ea8916b9ec1d52f2d66e804030d79f528f