DOCS-10310: opLatencies only for mongod

Author: kay-kim

source/reference/command/serverStatus.txt

@@ -753,6 +753,8 @@ network
 opLatencies
 ~~~~~~~~~~~
 
+*Only for ``mongod`` instances*
+
 .. code-block:: javascript
 
    "opLatencies" : {
@@ -766,6 +768,9 @@ opLatencies
    A document containing operation latencies for the database as a whole.
    See :ref:`latency-stats-document` for an description of this document.
 
+   Only :binary:`~bin.mongod` instances report
+   :serverstatus:`opLatencies`.
+
 .. serverstatus:: opLatencies.reads
 
    Latency statistics for read requests.