docs: add testing section to README

Author: ayunker

README.md

@@ -6,3 +6,21 @@ A friendly slack bot for announcing upcoming Hashrocket observed holidays and
 time off - communicating those in a timely manner makes us better consultants !
 
 Based on the Hashrocket Employee Handbook.
+
+## Testing
+
+The best way to verify the integration is to run the app locally, talking to
+Slack.
+
+You can change the channel in the `Announcer` in `lib/offbot/announcer.rb`, but
+keep in mind the channel must have the app installed to send messages.
+`#chicago` channel is a good test channel with fewer members to get spammed
+than `#general`.
+
+You'll need the api token from Heroku, it can be looked up via `heroku config`.
+
+To run the announcer locally:
+
+``` bash
+% SLACK_API_TOKEN=xxx bundle exec rake announce
+```