Add buy me a coffee button

README.md

@@ -1,6 +1,7 @@
 ## FCMBundle
 
 [![SensioLabsInsight](https://insight.sensiolabs.com/projects/c05b19ca-1d8b-4a3d-adf5-aa05a070a0cb/big.png)](https://insight.sensiolabs.com/projects/c05b19ca-1d8b-4a3d-adf5-aa05a070a0cb)
+<a href='https://ko-fi.com/A733TO5' target='_blank'><img height='36' style='border:0px;height:36px;' src='https://az743702.vo.msecnd.net/cdn/kofi2.png?v=0' border='0' alt='Buy Me a Coffee at ko-fi.com' /></a>
 
 This bundle's purpose is to make possible sending native notifications in mobile devices(Android and iOS) that use Google's **Firebase Cloud Messaging** service from a **Symfony2 Web App**.