def add
      unless domain = shift_argument
        error("Usage: heroku domains:add DOMAIN\nMust specify DOMAIN to add.")
      end
      validate_arguments!
      domain = action("Adding #{domain} to #{app}") do
        api.post_domains_v3_domain_cname(app, domain).body
      end
      output_with_bang "Configure your app's DNS provider to point to the DNS Target #{domain['cname']}"
      output_with_bang "For help, see https://devcenter.heroku.com/articles/custom-domains"
    end
def add
      unless domain = shift_argument
        error("Usage: heroku domains:add DOMAIN\nMust specify DOMAIN to add.")
      end
      validate_arguments!
      domain = action("Adding #{domain} to #{app}") do
        api.post_domains_v3_domain_cname(app, domain).body
      end
      output_with_bang "Configure your app's DNS provider to point to the DNS Target #{domain['cname']}"
      output_with_bang "For help, see https://devcenter.heroku.com/articles/custom-domains"
    end
domains:add DOMAIN

 add a custom domain to an app

Examples:

 $ heroku domains:add example.com
 Adding example.com to example... done

 !   Configure your app's DNS provider to point to the DNS Target example.herokuapp.com
 !   For help with custom domains, see https://devcenter.heroku.com/articles/custom-domains