Add build status badge

Author: felixmulder

README.md

@@ -1,5 +1,6 @@
 Dotty
 =====
+[![Build Status](http://dotty-ci.epfl.ch/api/badges/lampepfl/dotty/status.svg)](http://dotty-ci.epfl.ch/lampepfl/dotty)
 [![Join the chat at https://gitter.im/lampepfl/dotty](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/lampepfl/dotty?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 
 * [Homepage](http://dotty.epfl.ch)