Update ADMIN_TOKEN description in docs
Update ADMIN_TOKEN description in docs

Blurb taken from etc/keystone.conf.sample

partially fixes: bug #1283943

Change-Id: If7dac1dd902b52618f1af50a971fe1602426fdcf

ilay09/keystone,jamielennox/keystone,takeshineshiro/keystone,reeshupatel/demo,dims/keystone,jumpstarter-io/keystone,rushiagr/keystone,blueboxgroup/keystone,dims/keystone,UTSA-ICS/keystone-kerberos,jumpstarter-io/keystone,jonnary/keystone,UTSA-ICS/keystone-kerberos,dstanek/keystone,himanshu-setia/keystone,rajalokan/keystone,jonnary/keystone,vivekdhayaal/keystone,takeshineshiro/keystone,promptworks/keystone,klmitch/keystone,vivekdhayaal/keystone,cernops/keystone,rajalokan/keystone,roopali8/keystone,idjaw/keystone,mahak/keystone,nuxeh/keystone,rodrigods/keystone,ajayaa/keystone,MaheshIBM/keystone,openstack/keystone,ilay09/keystone,ajayaa/keystone,JioCloud/keystone,dstanek/keystone,himanshu-setia/keystone,jumpstarter-io/keystone,cernops/keystone,reeshupatel/demo,vivekdhayaal/keystone,maestro-hybrid-cloud/keystone,promptworks/keystone,dstanek/keystone,maestro-hybrid-cloud/keystone,nuxeh/keystone,ging/keystone,rajalokan/keystone,promptworks/keystone,mahak/keystone,mahak/keystone,klmitch/keystone,rushiagr/keystone,idjaw/keystone,nuxeh/keystone,rushiagr/keystone,blueboxgroup/keystone,openstack/keystone,jamielennox/keystone,rodrigods/keystone,openstack/keystone,ilay09/keystone,roopali8/keystone,MaheshIBM/keystone,ging/keystone,JioCloud/keystone,reeshupatel/demo