update incorrect whats new bullet (#281)

Author: jordan-smith721

source/whats-new.txt

@@ -57,8 +57,11 @@ The 3.0 driver release includes the following new features:
 
 - The ``IMongoClient`` interface inherits the ``IDisposable`` interface. As a result, the
   ``MongoClient`` class and other classes that implement the ``IMongoClient`` interface
-  contain a ``Dispose()`` method, which disposes of the underlying cluster and
-  connections to the MongoDB server. This implementation is experimental.
+  contain a ``Dispose()`` method, which disposes of the client. This method does not
+  dispose the underlying cluster and connections to the MongoDB server. To
+  dispose of the cluster and connections, call the
+  ``ClusterRegistry.UnregisterAndDisposeCluster()`` method. 
+  The implementation of the ``IDisposable`` interface is experimental.
 
   To learn more about the ``IDisposable`` interface and use of the
   ``Dispose()`` method, see