Superseded by https://github.com/thunderrabbit/new-DH-user-account
The following has been superseded by https://github.com/thunderrabbit/new-DH-user-account
From their panel -> Domains -> Manage Domains -> Add Hosting to a Domain / Sub-domain
fill in the blanks, including create a new user
Make sure the new user is a shell user at https://panel.dreamhost.com/index.cgi?tree=users.users