Slack Notifications only on select few workflow events

Hi Guys

I have turned on Slack notifications for my CircleCI project. This notifies me of all builds. But I only want notifications of when I deploy to production. This is a step in my workflow and only occurs after a manual step. I want to let people know when I deploy, but all the other events we already have a pretty good flow for.

Can anyone point me towards the documentation for this?