Update docs on adding a new app
Update docs on adding a new app

This now points to the block of port numbers in the `hieradata` rather
than the `development-vm/Procfile` file as that's been deprecated.

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet