Updated the intro paragraph of the README.md. 

'Gradle is build automation evolved' is to say nothing of meaning to new users.  When I was talking to people at Google I/O people were very confused about what Gradle *is*.  Many had already come to the independent conclusion that Gradle was a replacement for Jenkins.

We should be specific, Gradle is a build tool that happens to focus on build automation.  We should also make sure to list the languages and major software tools Gradle is designed to work with.