- add bash-completion files to autocomplete subcommands names

And maybe:
  - add a --destdir=<directory> option to the 'create-profile' command
  - in the 'new' command, set up a local composer repository like shown in
    https://github.com/drupal-composer/drupal-project/issues/249
  - add a --vanilla option to the 'new' command to skip any patching