Add Version Badge to README.md

Hello @timbunce.  We are making an effort to standardize the way developers discover CPAN distributions from Github repos.  We've had quite a bit of [success and support](http://badge.fury.io/projects) from package authors for other languages, and wanted to contribute to the Perl and CPAN community.

It looks a little different than the Travis CI old PNG badge until they switch to their [new design](http://blog.travis-ci.com/2014-03-20-build-status-badges-support-svg/).