Update README.md

Remove obsolete link

Author: MaggieKimani1

README.md

@@ -133,4 +133,4 @@ This project has adopted the [Microsoft Open Source Code of Conduct](https://ope
 For more information see the [Code of Conduct FAQ](https://opensource.microsoft.com/codeofconduct/faq/) or
 contact [[email protected]](mailto:[email protected]) with any additional questions or comments.
 
-To provide feedback and ask questions you can use Stack Overflow with the [OpenAPI.NET](https://stackoverflow.com/questions/tagged/openapi.net) tag or use the OpenAPI.NET Slack channel which you can join by registering for the HTTP APIs team at http://slack.httpapis.com.
+To provide feedback and ask questions you can use Stack Overflow with the [OpenAPI.NET](https://stackoverflow.com/questions/tagged/openapi.net) tag.