(DOCSP-14537): Clarify keyVaultClient description

Author: jeff-allen-mongo

source/reference/method/Mongo.txt

@@ -115,8 +115,7 @@ following parameters:
      - :method:`Mongo()` connection object.
 
      - *(Optional)* The MongoDB cluster hosting the key vault
-       collection. Omit to use the current database connection as the
-       key vault host.
+       collection.
 
        Specify a :method:`Mongo()` connection object pointing to the 
        cluster:
@@ -131,6 +130,11 @@ following parameters:
             "kmsProviders" : { ... }
           }
 
+       If ``keyVaultClient`` is omitted, the ``host`` specified to the
+       :method:`Mongo()` object containing the
+       ``ClientSideFieldLevelEncryptionOptions`` document is used as the
+       key vault host.
+
    * - ``keyVaultNamespace``
 
      - string