Update README

Author: philwebb

README.adoc

@@ -4,6 +4,7 @@
 This is the code accompanying the Livelessons video training course, https://www.safaribooksonline.com/library/view/building-microservices-with/9780134192468/[_Building Microservices with Spring Boot_],
 by http://twitter.com/starbuxman[Josh Long] and http://twitter.com/phillip_webb[Phil Webb]. 
 
+NOTE: We're currently upgrading this codebase for a second video. Please use the `v1` branch if you want to see the previous version.
 
 == Introduction
 What makes a modern application? A modern application lives on the web. It