Update the documentation link for doc migration
Update the documentation link for doc migration

This patch is proposed according to the Direction 10 of doc
migration(https://etherpad.openstack.org/p/doc-migration-tracking).

Change-Id: Ida0c34b7022e25196668038ac3499f7512b54786

openstack/python-brick-cinderclient-ext,openstack/python-brick-cinderclient-ext