Updated the intro paragraph of the README.md.  Saying that 'Gradle is build automation evolved' is to say nothing of meaning to new users.  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.
Merge pull request #161 from tobrien/doc-improvement

Updated the intro paragraph of the README.md.