slack invitation from the readme.md is not available.

[yangyshdan]

Please answer these questions before submitting your issue.

• Why do you submit this issue?
  bug

---

Bug

• Which version of SkyWalking, OS and JRE?
  readme.md

• Which company or project?
  School research project

• What happen?

The slack invitation link is broken from the readme.md

* Join `#skywalking` channel at [Apache Slack](https://join.slack.com/t/the-asf/shared_invite/enQtNDQ3OTEwNzE1MDg5LWY2NjkwMTEzMGI2ZTI1NzUzMDk0MzJmMWM1NWVmODg0MzBjNjAxYzUwMjIwNDI3MjlhZWRjNmNhOTM5NmIxNDk)

[wu-sheng]

Yes. Use this one, would you have interest to update document?

https://join.slack.com/t/the-asf/shared_invite/enQtNzc2ODE3MjI1MDk1LTAyZGJmNTg1NWZhNmVmOWZjMjA2MGUyOGY4MjE5ZGUwOTQxY2Q3MDBmNTM5YTllNGU4M2QyMzQ4M2U4ZjQ5YmY

[wu-sheng]

The link could be found here. https://cwiki.apache.org/confluence/display/INFRA/Slack+Guest+Invites