DOCS-158 clarification about use case and applicability

Author: Sam Kleinman

source/includes/note-conn-pool-stats.rst

@@ -1,4 +1,5 @@
 .. note::
 
    :dbcommand:`connPoolStats` only returns meaningful results for
-   :program:`mongos` program.
+   :program:`mongos` instances and for :program:`mongod` instances
+   in shard clusters.

source/reference/connection-pool-stats.txt

@@ -9,12 +9,15 @@ Synopsis
 
 :program:`mongos` instances maintain a pool of connections for
 interacting with constituent members of the :term:`shard clusters
-<shard cluster>`. The :dbcommand:`connPoolStats` command returns
-statistics regarding these connections between the :program:`mongos`
-and :program:`mongod` instances.
+<shard cluster>`. Additionally, :program:`mongod` instances maintain
+connection with other shards in the cluster for migrations. The
+:dbcommand:`connPoolStats` command returns statistics regarding these
+connections between the :program:`mongos` and :program:`mongod`
+instances or between the :program:`mongod` instances in a shard
+cluster.
 
 .. include:: /includes/note-conn-pool-stats
-
+..
 Output
 ------