Included new section to 'Create and manage roles' in Admin User Guide

New section to the Admin User guide to 'Create and manage roles'
in the dashboard chapter.
Partial-Bug: #1279133

Change-Id: Icb3667a6a83d37a84f649d1e01171a3f569a4f2d
Merge "Included new section to 'Create and manage roles' in Admin User Guide"