Add a deploy message for how to run end to end testing

Test Plan:
- I couldn't actually get this to work correctly but I followed some
  steps on the infrastructure room to no avail. Not including it here
  in case there is info that shouldn't be shared on github.
- After that I ran deploy_pipeline.py --hipchat_sender=Mr\ Gorilla
  manual-test and it says unknown user

Reviewers: csilvers

Reviewed By: csilvers

Subscribers: jlfwong

Differential Revision: https://phabricator.khanacademy.org/D14773