message: Refine documentation on disabling the URL launcher
diff: # This program is executed when clicking on a text which is recognized as a URL.
  # The URL is always added to the command as the last parameter.
  #
  - # When set to `None`, URL launching will be disabled completely.
  + # When set to `launcher: None`, URL launching will be disabled completely.
  #
  # Default:
  # - (macOS) open
  