Add circleci build status badge

README.md

@@ -1,4 +1,4 @@
-![nginx 1.9.5](https://img.shields.io/badge/nginx-1.9.5-brightgreen.svg) ![License MIT](https://img.shields.io/badge/license-MIT-blue.svg)
+![nginx 1.9.5](https://img.shields.io/badge/nginx-1.9.5-brightgreen.svg) ![License MIT](https://img.shields.io/badge/license-MIT-blue.svg) ![Build](https://circleci.com/gh/jwilder/nginx-proxy.svg?&style=shield&circle-token=2da3ee844076a47371bd45da81cf27409ca7306a)
 
 nginx-proxy sets up a container running nginx and [docker-gen][1].  docker-gen generates reverse proxy configs for nginx and reloads nginx when containers are started and stopped.