Slack Invite

Add link to Slack channel invite in footer

Author: cnlee1702

_config.yml

@@ -69,6 +69,8 @@ social:
     url: https://www.facebook.com/PythonFrederick/
   - title: meetup
     url: https://www.meetup.com/python-frederick/
+  - title: slack
+    url: https://fredericktechinvite.herokuapp.com/ 
 
 # Postal address (add as many lines as necessary)
 address: