Add description to auto_deployment

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) :) .