Release notes for 2.3.0-beta1.

Author: rstam

Release Notes/Release Notes v2.3.0.md

@@ -1,3 +1,18 @@
-# .NET Driver Version 2.3.0 Release Notes
+# .NET Driver Version 2.3.0-beta1 Release Notes (PRE-RELEASE)
 
-This is placeholder for release notes for the next version.
+This is a minor release consisting of:
+
+1. Bug fixes since 2.2.4 was released
+2. Support for .NET Core
+
+An online version of these release notes is available at:
+
+https://github.com/mongodb/mongo-csharp-driver/blob/master/Release%20Notes/Release%20Notes%20v2.3.0.md
+
+The JIRA tickets resolved in this release is available at:
+
+https://jira.mongodb.org/issues/?jql=project%20%3D%20CSHARP%20AND%20fixVersion%20%3D%202.3%20ORDER%20BY%20key%20ASC
+
+Upgrading
+
+We don't believe there are any breaking changes in this release.