DOCS-10060 add comment to truncated command field

Signed-off-by: kay <kay.kim@10gen.com>

source/includes/extracts-command-field.yaml

@@ -5,9 +5,21 @@ content: |
   
   A document containing the full command object associated with this
   operation. If the command document exceeds {{truncThreshold}}, the
-  value is a string summary of the object. If the string summary
-  exceeds {{truncThreshold}}, the string summary is truncated, denoted
-  with an ellipsis (...) at the end of the string.
+  document has the following form:
+
+  .. code-block:: javascript
+
+     "command" : {
+       "$truncated": <string>,
+       "comment": <string>
+     }
+
+  The ``$truncated`` field contains a string summary of the document excluding
+  the document's ``comment`` field if present. If the summary still exceeds
+  {{truncThreshold}} then it is further truncated, denoted by an ellipsis
+  (...) at the end of the string.
+
+  The ``comment`` field is present if a comment was passed to the operation.
   
   The following example output contains the command object for a
   :doc:`find </reference/method/db.collection.find/#db.collection.find>`