DOCS-557 add note to convertToCapped

source/reference/command/convertToCapped.txt

@@ -7,21 +7,41 @@ convertToCapped
 .. dbcommand:: convertToCapped
 
    The :dbcommand:`convertToCapped` command converts an existing,
-   non-capped collection to a :term:`capped collection`. Use the
-   following syntax:
+   non-capped collection to a :term:`capped collection`.
+
+   The command has the following syntax:
 
    .. code-block:: javascript
 
-      {convertToCapped: "collection", size: 100 * 1024 }
+      {convertToCapped: <collection>, size: <capped size> }
+
+   This command coverts an existing ``collection`` to a capped
+   collection with a maximum size specified by the ``capped size`` in
+   bytes.
+
+   During the conversion, the :dbcommand:`convertToCapped` command
+   exhibit the following behavior:
+
+   - The documents in the original collection will be traversed in
+     :term:`$natural order <natural order>` and loaded into a new
+     capped collection.
 
-   This command coverts ``collection``, an existing collection, to a
-   capped collection, with a maximum size of 100 KB. This command
-   accepts the ``size`` and ``max`` options. See the
-   :dbcommand:`create` command for additional details.
+   - If the ``capped size`` specified for the capped collection is
+     smaller than the size of the original uncapped collection, then
+     the documents will be aged out of the collection based on
+     insertion order(First In, First Out).
+
+   .. note::
+
+      The :dbcommand:`convertToCapped` command is not supported in a
+      sharded cluster.
 
    .. warning::
 
       The :dbcommand:`convertToCapped` will not recreate indexes from
       the original collection on the new collection. If you need
       indexes on this collection you will need to create these indexes
       after the conversion is complete.
+
+   .. seealso:: :dbcommand:`create`
+