Merge pull request mongodb#181 from mcmorisi/DRIVERS-2658-hint

DOCSP-45139: Add Hint option for Distinct operation

Author: mcmorisi

source/read/distinct.txt

@@ -138,6 +138,10 @@ options you can set to customize the operation:
      - | The read preference to use for the operation. To learn more, see
          :manual:`Read Preference </core/read-preference/>` in the Server manual.
        | **Type**: ``MongoDB\Driver\ReadPreference``
+   
+   * - ``hint``
+     - | The index to use for the operation.
+       | **Type**: ``string|object``
 
 The following example retrieves the distinct values of the ``name`` field for
 all documents that have a ``borough`` field value of ``'Bronx'`` and a