Update README.md

Add HHVM tested seal of approval

Author: sabberworm

README.md

@@ -1,7 +1,7 @@
 PHP CSS Parser
 --------------
 
-[![build status](https://travis-ci.org/sabberworm/PHP-CSS-Parser.png)](https://travis-ci.org/sabberworm/PHP-CSS-Parser)
+[![build status](https://travis-ci.org/sabberworm/PHP-CSS-Parser.png)](https://travis-ci.org/sabberworm/PHP-CSS-Parser) [![HHVM Status](http://hhvm.h4cc.de/badge/sabberworm/php-css-parser.png)](http://hhvm.h4cc.de/package/sabberworm/php-css-parser)
 
 A Parser for CSS Files written in PHP. Allows extraction of CSS files into a data structure, manipulation of said structure and output as (optimized) CSS.