doc: Upgrade steps for quota

Change-Id: I6701cba911665cfefa1984c0441701a3354635d6
BUG: 969461
Signed-off-by: Krutika Dhananjay <kdhananj@redhat.com>
Reviewed-on: http://review.gluster.org/6438
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>