README says Java 6; code runs on Java 7

[jbrains]

I'd like to clarify the README, but I don't want to revise history until I've drafted the entire book once.

As of snapshot 640, the project builds and runs with Java 6 and Java 7.

What makes the README confusing: IDEA runs on Java 6 on my Mac, but the project runs on Java 7. Sorry.