docs: def do_blacklist(config, config_dir):
      """
      CLI action "run editor for blacklist".
      """
      if not os.path.exists(config_dir):
          print "Configuration '{}' does not exist.".format(config)
          exit(1)    
  
      editor = os.environ["EDITOR"]
  
      config_blacklist = os.path.join(config_dir, 'blacklist')
      call([editor, config_blacklist])
      print "Blacklist configuration has been updated."