chore: Added slack channel

Author: martoc

README.md

@@ -2,6 +2,7 @@
 [![Go Report Card](https://goreportcard.com/badge/github.com/martoc/gcp-kafka-auth-handler)](https://goreportcard.com/report/github.com/martoc/gcp-kafka-auth-handler)
 ![Go Version](https://img.shields.io/github/go-mod/go-version/martoc/gcp-kafka-auth-handler/main)
 [![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)
+[![slack](https://img.shields.io/badge/slack-general-brightgreen.svg?logo=slack)](https://app.slack.com/messages/T8L8AAD3M/C8LBHLSVA)
 
 # gcp-kafka-auth-handler