Add build icon to README

README.md

@@ -2,6 +2,8 @@
 
 # Running The Tests
 
+[![Build Status](https://api.travis-ci.org/dw/mitogen.svg?branch=master)](https://api.travis-ci.org/dw/mitogen)
+
 Your computer should have an Internet connection, and the ``docker`` command
 line tool should be able to connect to a working Docker daemon (localhost or
 elsewhere for OS X etc.) that can run new images.