add DolphinScheduler slack channel (#2519)

* add DolphinScheduler slack channel

* Update README.md
Co-Authored-By: NJiajie Zhong <zhongjiajie955@hotmail.com>
Co-authored-by: NJiajie Zhong <zhongjiajie955@hotmail.com>
Co-authored-by: Nqiaozhanwei <qiaozhanwei@outlook.com>

README.md

@@ -99,9 +99,9 @@ It is because of the shoulders of these open source projects that the birth of t
 ### Get Help
 1. Submit an issue
 1. Subscribe the mail list : https://dolphinscheduler.apache.org/en-us/docs/development/subscribe.html.  then send mail to dev@dolphinscheduler.apache.org
+1. Slack channel: [![Slack Status](https://img.shields.io/badge/slack-join_chat-white.svg?logo=slack&style=social)](https://join.slack.com/share/zt-do3gvfhj-UUhrAX2GxkVX_~JJt1jpKA)
 1. Contact WeChat(dailidong66). This is just for Mandarin(CN) discussion.
 
 ### License
 Please refer to [LICENSE](https://github.com/apache/incubator-dolphinscheduler/blob/dev/LICENSE) file.
 
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