docs(README): connect to Fine Uploader gitter room

Author: rnicholus

README.md

@@ -1,4 +1,6 @@
 # php-s3-server
+[![Gitter](https://img.shields.io/gitter/room/nwjs/nw.js.svg?maxAge=2592000)](https://gitter.im/FineUploader?utm_source=share-link&utm_medium=link&utm_campaign=share-link)
+
 PHP-based server-side example for handling signature, delete, etc endpoint requests from Fine Uploader S3.
 
 You can pull down this from packagist via composer! The package name is `fineuploader/php-s3-server`.