Use #writefreely badge, not Slack

Author: thebaer

README.md

@@ -2,7 +2,7 @@ Write.as web core
 =================
 [![GoDoc](https://godoc.org/github.com/writeas/web-core?status.svg)](https://godoc.org/github.com/writeas/web-core)
 [![Build Status](https://travis-ci.org/writeas/web-core.svg)](https://travis-ci.org/writeas/web-core)
-[![Public Slack discussion](http://slack.write.as/badge.svg)](http://slack.write.as/)
+[![#writefreely on freenode](https://img.shields.io/badge/freenode-%23writefreely-blue.svg)](http://webchat.freenode.net/?channels=writefreely)
 [![Discuss on our forum](https://img.shields.io/discourse/https/discuss.write.as/users.svg?label=forum)](https://discuss.write.as/c/development)
 
 web-core holds components of the [Write.as](https://write.as) web application.