docs(Assistant V2): Added Assistant V2 private beta note

Author: mediumTaj

src/IBM.WatsonDeveloperCloud.Assistant.v2/README.md

@@ -2,6 +2,8 @@
 
 ### Assistant
 
+**Watson Assistant v2 API is released in beta. For details, see the ["Introducing Watson Assistant"](https://www.ibm.com/blogs/watson/2018/03/the-future-of-watson-conversation-watson-assistant/) blog post.**
+
 The IBM Watson™ [Assistant][assistant] service combines machine learning, natural language understanding, and integrated dialog tools to create conversation flows between your apps and your users.
 
 ### Installation