Added Release Notes for 2.2.3.

Release Notes/Release Notes v2.2.3.md

@@ -1,3 +1,21 @@
 # .NET Driver Version 2.2.3 Release Notes
 
-This is file is a placeholder.
+This is a patch release which fixes a bug reported since 2.2.2 was released.
+
+This is a recommended upgrade if you are using ReadPreferences with a sharded cluster (i.e. connecting through mongos).
+
+An online version of these release notes is available at:
+
+https://github.com/mongodb/mongo-csharp-driver/blob/v2.2.x/Release%20Notes/Release%20Notes%20v2.2.3.md
+
+Only one issue was fixed in this release:
+
+https://jira.mongodb.org/browse/CSHARP-1537
+
+Documentation on the .NET driver can be found at:
+
+http://mongodb.github.io/mongo-csharp-driver/
+
+Upgrading
+
+There are no known backwards breaking changes in this release.