Add description to auto_deployment

[pcasaretto]

Hey atmos,

Today I received some unexpected deploy notifications on Slack and it took me some time to find out they were originating from the auto-deploy mechanism.
For some reason I thought I had to activate, or opt-in somehow for it to work.
IMHO having it active by default is a bit dangerous. Because we use a non-orthodox branching flow, I was lucky I had not configured the production enviroment on hubot.
This PR adds a description to the deployment so it's easier to track it back. (And allowed me to express my concerns) :) .

[atmos]

Doh, sorry about that. Thanks for the fix.

[pcasaretto]

What if we added an env variable to control if auto deployments are enabled?

[atmos]

I was hoping to put auto-deployment information in the apps.json from hubot-deploy for now. We can parse it out of the payload and look it up in the Deployments table. This way you can do auto-deployment on a per app level.

[pcasaretto]

I knew you had a much better idea. :)
I'm not sure how you handle releases, but to keep things from breaking, I suggest we assume auto-deployment is true if the key is missing (and mention that on the README).

[atmos]

Yeah, more stable releases will come once the original feature set stabilizes. We should definitely document the behavior.

[pcasaretto]

There is a problem with this approach. Changing the auto-deployment config would require deploying hubot itself and issuing a new deploy for the app so the new payload will reach heaven.

[atmos]

Yup, for now it's sub-optimal but something we can fix in the future. I'd like for the apps.json in hubot to be configurable via chatops too. The apps.json stuff was a stop gap to get all the pieces going before hopefully looking back at hubot and seeing how to make everything easier once it's in place.