MB-10697: Add upr stats to stats.org docs file

Change-Id: I03120b0cac52152b82120f67ac56bed3648e8378
Reviewed-on: http://review.couchbase.org/38157
Reviewed-by: Sriram Ganesan <sriram@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>