Add userdoc install instructions for RDO

Change-Id: I553f9733b77235e89d69b6e18f02094fc46b9ba1
Add pointer to userdoc from horizon guide

Change-Id: Ie55edace1a95ff6c4f698af90987da1493d8c18c
Add horizon install instructions for RDO

Change-Id: Id057c2d81688fb3c8e5bbe490e2059deb9fb5273
Merge "Add userdoc install instructions for RDO"
Merge "Add pointer to userdoc from horizon guide"
Merge "Add horizon install instructions for RDO"