Announce HHVM 3.5+ support [skip ci]

Author: thekid

README.md

@@ -6,6 +6,7 @@ RDBMS support for the XP Framework
 [![BSD Licence](https://raw.githubusercontent.com/xp-framework/web/master/static/licence-bsd.png)](https://github.com/xp-framework/core/blob/master/LICENCE.md)
 [![Required PHP 5.4+](https://raw.githubusercontent.com/xp-framework/web/master/static/php-5_4plus.png)](http://php.net/)
 [![Supports PHP 7.0+](https://raw.githubusercontent.com/xp-framework/web/master/static/php-7_0plus.png)](http://php.net/)
+[![Supports HHVM 3.5+](https://raw.githubusercontent.com/xp-framework/web/master/static/hhvm-3_5plus.png)](http://hhvm.com/)
 [![Latest Stable Version](https://poser.pugx.org/xp-framework/rdbms/version.png)](https://packagist.org/packages/xp-framework/rdbms)
 
 RDBMS access APIs, connection manager, reverse engineering, O/R mapping.