Install Guide: admin-openrc.sh is prerequisite
Install Guide: admin-openrc.sh is prerequisite

Mention admin-openrc.sh as prerequisite as well.

Change-Id: Ie47e23230a40630e0d87a6371edd67cf11305a7a
Closes-Bug: #1443896

Akasurde/openstack-manuals,kairoaraujo/openstack-manuals,kairoaraujo/openstack-manuals,Akasurde/openstack-manuals,openstack/openstack-manuals,gongysh2004/openstack-manual,openstack/openstack-manuals,potsmaster/openstack-manuals,saeki-masaki/openstack-manuals,gongysh2004/openstack-manual,saeki-masaki/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,openstack/openstack-manuals,potsmaster/openstack-manuals,openstack/openstack-manuals