DOCSP-44237 flags Option deprecation on v2.21

Author: lindseymoore

source/reference/method/MongoDBDatabase-createCollection.txt

@@ -152,6 +152,12 @@ Parameters
          :manual:`db.createCollection()
          </reference/method/db.createCollection>` for more information.
 
+         *Deprecated*: This option is deprecated and will be removed in 
+         {+php-library+} v2.0. For more information on upgrading from the MMAPv1 storage 
+         engine to Wired Tiger, see the 
+         :manual:`Change a Self-Managed Standalone to WiredTiger </tutorial/change-standalone-wiredtiger/>` 
+         guide.
+
      * - indexOptionDefaults
        - array|object
        - Allows users to specify a default configuration for indexes when