Added link to the slackin icon

Author: dkapanidis

README.md

@@ -24,7 +24,7 @@ docker pull mhart/alpine-node:latest
 * During workshop the following ports are used: `80`, `8088` and the range `4000-4010`. If they are not available on your machine, adjust the CLI commands accordingly.
 
 ### Chat
-![Members online on Docker Barcelona Slack](https://dockerbcn.herokuapp.com/badge.svg)
+[![Members online on Docker Barcelona Slack](https://dockerbcn.herokuapp.com/badge.svg)](https://dockerbcn.herokuapp.com)
 
 Join [Docker Barcelona Slack](https://dockerbcn.herokuapp.com)!