Added Gitter badge

Author: gitter-badger

README.md

@@ -1,4 +1,6 @@
 # php-annotations
+
+[![Join the chat at https://gitter.im/php-annotations/php-annotations](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/php-annotations/php-annotations?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 [![Build Status](https://travis-ci.org/php-annotations/php-annotations.svg?branch=master)](https://travis-ci.org/php-annotations/php-annotations)
 [![Scrutinizer Quality Score](https://scrutinizer-ci.com/g/php-annotations/php-annotations/badges/quality-score.png?s=41628593655dae3740c3a64f172438430ee26b84)](https://scrutinizer-ci.com/g/php-annotations/php-annotations/)
 [![Code Coverage](https://scrutinizer-ci.com/g/php-annotations/php-annotations/badges/coverage.png?s=dbea8860e011cdb7b5352b48c25259ca950fe2c6)](https://scrutinizer-ci.com/g/php-annotations/php-annotations/)