doc: Add Dingtalk group QR code in README.md (#292)

Author: binbin0325

README.md

@@ -43,4 +43,7 @@ For bug report, questions and discussions please submit [GitHub Issues](https://
 
 Contributions are always welcomed! Please see [CONTRIBUTING](./CONTRIBUTING.md) for detailed guidelines.
 
-You can start with the issues labeled with [`good first issue`](https://github.com/alibaba/sentinel-golang/issues?q=is%3Aissue+is%3Aopen+label%3A%22good+first+issue%22).
+You can start with the issues labeled with [`good first issue`](https://github.com/alibaba/sentinel-golang/issues?q=is%3Aissue+is%3Aopen+label%3A%22good+first+issue%22).
+
+## Communication
+![Sentinel Go Group QR Code](https://user-images.githubusercontent.com/28588342/96000984-19f8f380-0e6a-11eb-95ab-72594cd2673b.jpg)