Add badge to show number of project installations

Author: PaulRotmann

README.md

@@ -1,4 +1,7 @@
-# clue/sse-react [![Build Status](https://travis-ci.org/clue/php-sse-react.svg?branch=master)](https://travis-ci.org/clue/php-sse-react)
+# clue/sse-react 
+
+[![Build Status](https://travis-ci.org/clue/php-sse-react.svg?branch=master)](https://travis-ci.org/clue/php-sse-react)
+[![installs on Packagist](https://img.shields.io/packagist/dt/clue/sse-react?color=blue&label=installs%20on%20Packagist)](https://packagist.org/packages/clue/sse-react)
 
 Streaming, async HTML5 Server-Sent Events server (aka. SSE or EventSource), built on top of [React PHP](http://reactphp.org/).