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

Change-Id: I5826faf0f6a39d3690727894da6a360613aed824
Reviewed-on: http://review.couchbase.org/38158
Reviewed-by: Sriram Ganesan <sriram@couchbase.com>
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>