Update README.md

cloudwebrtc · web-flow · commit bf318ed6b8f5 · 2021-05-05T19:25:39.000+08:00
diff --git a/README.md b/README.md
@@ -1,4 +1,5 @@
 # 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

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`@@ -1,4 +1,5 @@`
`1`	`1`	`# callkeep`
	`2`	`+ [![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)`
`2`	`3`
`3`	`4`	`* iOS CallKit and Android ConnectionService for Flutter`
`4`	`5`	`* Support FCM and PushKit`