Add Slack Badges to README.md

Closes #493

Author: fmichonneau

README.md

@@ -1,3 +1,6 @@
+[![Create a Slack Account with us](https://img.shields.io/badge/Create_Slack_Account-The_Carpentries-071159.svg)](https://swc-slack-invite.herokuapp.com/)
+ [![Slack Status](https://img.shields.io/badge/Slack_Channel-swc--py--inflammation-E01563.svg)](https://swcarpentry.slack.com/messages/C9Y0L6MF0) 
+
 python-novice-inflammation
 ==========================