Update README.md

Add "Buy me a coffee" button on the README.md

README.md

@@ -1,5 +1,8 @@
 # flutter_background
 
+[!["Buy Me A Coffee"](https://www.buymeacoffee.com/assets/img/custom_images/orange_img.png)](https://www.buymeacoffee.com/julianassmann)
+
+
 A plugin to keep flutter apps running in the background. Currently only works with Android.
 
 It achieves this functionality by running an [Android foreground service](https://developer.android.com/guide/components/foreground-services) in combination with a [partial wake lock](https://developer.android.com/training/scheduling/wakelock#cpu) and [disabling battery optimizations](https://developer.android.com/training/monitoring-device-state/doze-standby#support_for_other_use_cases) in order to keep the flutter isolate running.