Slack channel naming conventions

Having some conventions in how to name Slack channels makes them easier to find, and makes it easy to figure out what a channel is for.

• #team- for team channels, e.g. #team-zebra.

• #proj- for projects (but not products, because a project is not a product).

• #z- for off-topic stuff, e.g. #z-food.

• #help- for support channels, e.g. #help-deploy for help in getting stuff deployed.

• #craft- for craft channels, e.g. #craft-ruby for Ruby stuff or #craft-frontend for general frontend stuff.

• #office- for office-specific channels, like #office-berlin for the Berlin office.