update what's new

Author: mongoKart

source/whats-new.txt

@@ -152,6 +152,9 @@ The 3.0 driver release includes the following new features:
   To learn more about using the aggregation pipeline with the {+driver-short+}, see
   :ref:`csharp-aggregation`.
 
+- Adds an API for bulk write operations. To learn more about bulk write operations, see
+  :ref:`csharp-bulk-write`.
+
 For more information about this release, see the :github:`v3.0 release notes
 </mongodb/mongo-csharp-driver/releases/tag/v3.0.0>`.