Update README.md

README.md

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 # callkeep
- [![slack](https://img.shields.io/badge/join-us%20on%20slack-gray.svg?longCache=true&logo=slack&colorB=brightgreen)](https://join.slack.com/t/flutterwebrtc/shared_invite/zt-q83o7y1s-FExGLWEvtkPKM8ku_F8cEQ)
+
+[![Financial Contributors on Open Collective](https://opencollective.com/flutter-webrtc/all/badge.svg?label=financial+contributors)](https://opencollective.com/flutter-webrtc) [![pub package](https://img.shields.io/pub/v/callkeep.svg)](https://pub.dartlang.org/packages/callkeep) [![slack](https://img.shields.io/badge/join-us%20on%20slack-gray.svg?longCache=true&logo=slack&colorB=brightgreen)](https://join.slack.com/t/flutterwebrtc/shared_invite/zt-q83o7y1s-FExGLWEvtkPKM8ku_F8cEQ)
 
 * iOS CallKit and Android ConnectionService for Flutter
 * Support FCM and PushKit