Add link to v2 migration document in readme for main branch (Azure#2880)

readme.md

@@ -1,5 +1,13 @@
 # Microsoft Azure IoT SDK for .NET
 
+## V2 clients release notice
+
+The [2.0.0-preview001](https://github.com/Azure/azure-iot-sdk-csharp/releases/tag/2022-10-14-v2preview) release has been published for each package in this library. 
+These packages simplify usage and handling of our clients, and we highly encourage you to try out these packages and share your feedback. Once we promote these 
+changes to `main` in the future and release the 2.x.x packages publicly, all future features will be brought only to this new major version.
+
+If you need any help migrating your code to try out the new 2.X.X clients, please see this [migration guide](https://github.com/Azure/azure-iot-sdk-csharp/blob/previews/v2/SDK%20v2%20migration%20guide.md).
+
 ## Contents
 
 This repository contains the following: