Preview: Documenting config.json settings (pre-Mattermost v1.0)

Thanks @alerque, highly appreciate both the Arch Linux package and all your help and interest in Mattermost so far. We have an early draft of production install instructions outside of Docker and are sequencing documentation in the product for after the admin console is setup, since there’s been some refactoring of config files for Oct 2 release.

Docker was a good starting point, completely agree bare metal installs are a priority.