Refer to extension docs for Client::startSession() options

docs/includes/apiargs-MongoDBClient-method-startSession-option.yaml

-arg_name: option
-name: causalConsistency
-type: boolean
-description: |
-  Enables or disables :ref:`causal consistency <causal-consistency>` for the
-  session. If true, each operation in the session will be causally ordered after
-  the previous read or write operation. Set to false to disable causal
-  consistency. Defaults to true.
-interface: phpmethod
-operation: ~
-optional: true
-...

docs/reference/method/MongoDBClient-startSession.txt

@@ -23,14 +23,14 @@ Definition
 
       function startSession(array $options = []): MongoDB\Driver\Session
 
-   The ``$options`` parameter supports the following options:
-
-   .. include:: /includes/apiargs/MongoDBClient-method-startSession-option.rst
+   Refer to the :php:`MongoDB\\Driver\\Manager::startSession()
+   <mongodb-driver-manager.startsession>` extension reference for accepted
+   options.
 
 Return Values
 -------------
 
-A :php:`MongoDB\Driver\Session <mongodb-driver-session>`
+A :php:`MongoDB\Driver\Session <mongodb-driver-session>` object.
 
 Errors/Exceptions
 -----------------