docs: add link to slack channel

Author: jirfag

README.md

@@ -1308,6 +1308,8 @@ Existing debug tags:
 
 ## Contact Information
 
+Slack channel: [#golangci-lint](https://slack.com/share/IS0TDK8RG/TEKQWjTZXxfK9Ta2G5HrnsMY/enQtODg0OTMxNjU0ODY2LWUyMTQ3NDc2MmNlNGU3NTNhYWE0Nzc3MjUyZjkxZWI3YjI5ODMwNDA1NTU3MmM2Yzc5ZjQyYTFkNThlODllN2Y).
+
 You can contact the [author](https://github.com/jirfag) of GolangCI-Lint
 by [[email protected]](mailto:[email protected]). Follow the news and releases on our [twitter](https://twitter.com/golangci) and our [blog](https://medium.com/golangci).
 

README.tmpl.md

@@ -651,6 +651,8 @@ Existing debug tags:
 
 ## Contact Information
 
+Slack channel: [#golangci-lint](https://slack.com/share/IS0TDK8RG/TEKQWjTZXxfK9Ta2G5HrnsMY/enQtODg0OTMxNjU0ODY2LWUyMTQ3NDc2MmNlNGU3NTNhYWE0Nzc3MjUyZjkxZWI3YjI5ODMwNDA1NTU3MmM2Yzc5ZjQyYTFkNThlODllN2Y).
+
 You can contact the [author](https://github.com/jirfag) of GolangCI-Lint
 by [[email protected]](mailto:[email protected]). Follow the news and releases on our [twitter](https://twitter.com/golangci) and our [blog](https://medium.com/golangci).