docs: add notice for 2.x

README.md

@@ -34,6 +34,9 @@ used in the world's biggest online commerce company [Alibaba](http://www.alibaba
 * [Migrating from node_redis](https://github.com/luin/ioredis/wiki/Migrating-from-node_redis)
 * [Error Handling](#error-handling)
 
+# v2.0
+2.0 is under active development. Checkout the [2.x branch](https://github.com/luin/ioredis/pull/246) to see whether it contains the feature you need.
+
 <hr>
 <a href="https://itunes.apple.com/app/medis-gui-for-redis/id1063631769"><img align="right" src="medis.png" alt="Download on the App Store"></a>