add jenkins badge

Signed-off-by: Morgan Bauer <[email protected]>

Author: MHBauer

README.md

@@ -1,6 +1,7 @@
 # Swarm: a Docker-native clustering system
 
 [![GoDoc](https://godoc.org/github.com/docker/swarm?status.png)](https://godoc.org/github.com/docker/swarm)
+[![Jenkins Build Status](https://jenkins.dockerproject.org/view/Swarm/job/Swarm%20Master/badge/icon)](https://jenkins.dockerproject.org/view/Swarm/job/Swarm%20Master/)
 [![Build Status](https://travis-ci.org/docker/swarm.svg?branch=master)](https://travis-ci.org/docker/swarm)
 [![Coverage Status](https://coveralls.io/repos/docker/swarm/badge.svg)](https://coveralls.io/r/docker/swarm)