Release notes for 2.9.0-beta2.

Author: rstam

Release Notes/Release Notes v2.9.0-beta2.md

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+# .NET Driver Version 2.9.0-beta2 Release Notes
+
+This is a beta release for the 2.9.0 version of the driver that will be released with MongoDB server version 4.2.
+
+The main features in 2.9.0-beta2 are:
+
+* Sharded transactions using the same API as replica set transactions
+* Convenient API for transactions
+* Support for message compression
+* SRV polling for mongodb+srv connection scheme
+* Retryable reads on by default
+* Retryable writes on by default
+* Update specification using an aggregation framework pipeline
+
+An online version of these release notes is available at:
+
+https://github.com/mongodb/mongo-csharp-driver/blob/master/Release%20Notes/Release%20Notes%20v2.9.0-beta2.md
+
+The full list of JIRA issues that are currently scheduled to be resolved in this release is available at:
+
+https://jira.mongodb.org/issues/?jql=project%20%3D%20CSHARP%20AND%20fixVersion%20%3D%202.9.0%20ORDER%20BY%20key%20ASC
+
+The list may change as we approach the release date.
+
+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.