Merge pull request #51 from pomerium/kenjenkins/readme

readme: replace Slack badge with Discuss link

Author: kenjenkins

README.md

@@ -3,7 +3,7 @@
 [![Go Report Card](https://goreportcard.com/badge/github.com/pomerium/autocache)](https://goreportcard.com/report/github.com/pomerium/autocache)
 [![GoDoc](https://godoc.org/github.com/pomerium/autocache?status.svg)](https://godoc.org/github.com/pomerium/autocache)
 [![LICENSE](https://img.shields.io/github/license/pomerium/autocache.svg)](https://github.com/pomerium/autocache/blob/master/LICENSE)
-[![pomerium chat](https://img.shields.io/badge/chat-on%20slack-blue.svg?style=flat&logo=slack)](http://slack.pomerium.io)
+[![discuss](https://img.shields.io/discourse/posts?server=https%3A%2F%2Fdiscuss.pomerium.com%2F&label=discuss)](https://discuss.pomerium.com/)
 
 # Autocache