Link to wg-api-expression slack and mailing-list

Author: nodo

README.md

@@ -57,8 +57,8 @@ Learn how to engage with the Kubernetes community on the [community page](http:/
 
 You can reach the maintainers of this project at:
 
-- [Slack](http://slack.k8s.io/)
-- [Mailing List](https://groups.google.com/forum/#!forum/kubernetes-wg-apply)
+- Slack: [#wg-api-expression](https://kubernetes.slack.com/messages/wg-api-expression)
+- [Mailing List](https://groups.google.com/forum/#!forum/kubernetes-wg-api-expression)
 
 ### Code of conduct