DOCSP-28763 FAQ for slow operations warnings (#119)

* DOCSP-28763 Adds slow operation FAQ entry

* Adjusts text

* Adjusts text

* Adjusts text

* Adjusts text

* Fixes per Jeff Allen

Author: kennethdyer

source/faq.txt

@@ -107,3 +107,20 @@ have more than 2 non-arbiter nodes and you must sync from a non-arbiter
 node. Use the source cluster's connection string to specify a
 :ref:`read preference <mongodb-uri>` for a non-arbiter, data-bearing
 node. 
+
+What if I see a Slow Operation Warning?
+---------------------------------------
+
+Slow operation warnings can occur during the initial sync or the application 
+of a change event when there is a slow read operation on the source cluster 
+or a slow write operation on the destination cluster.  The warning may
+indicate network congestion or resource strain on the source or destination
+cluster.
+
+While these warnings do not indicate failures in themselves, slow operations
+can cause operation timeout errors in ``mongosync`` and migration failures.
+
+If you see slow operation warnings, check CPU, memory, and network usage on the
+source and destination clusters.  If the clusters are underprovisioned for your
+needs, consider upgrading the cluster hardware.
+