DOCS-642 clarifying affect of shardsvr

Author: Sam Kleinman

source/reference/configuration-options.txt

@@ -739,7 +739,8 @@ Sharding Cluster Options
 
    Set this value to ``true`` to configure this :program:`mongod`
    instance as a shard in a partitioned cluster. The default port for
-   these instances is ``27018``.
+   these instances is ``27018``. The only affect of
+   :setting:`shardsvr` is to change the port number.
 
 .. setting:: noMoveParanoia
 

source/reference/mongod.txt

@@ -574,7 +574,9 @@ Sharding Cluster Options
 .. option:: --shardsvr
 
    Configures this :program:`mongod` instance as a shard in a
-   partitioned cluster. The default port for these instances is ``27018``.
+   partitioned cluster. The default port for these instances is
+   ``27018``.  The only affect of :option:`--shardsvr` is to change
+   the port number.
 
 .. option:: --noMoveParanoia