doc: Upgrade steps for quota

Change-Id: Ib007029f74f52d28e424a15950d46504336bde10
BUG: 969461
Signed-off-by: Krutika Dhananjay <kdhananj@redhat.com>
Reviewed-on: http://review.gluster.org/7419
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>