old_contents: # Copyright 2019 The LUCI Authors. All rights reserved.
  # Use of this source code is governed under the Apache License, Version 2.0
  # that can be found in the LICENSE file.
  
  """Generate documentation from the recipes and modules in the current repo.
  
  This can output as a protobuf of various forms (JSON, Text or binary), using the
  `Doc` message in `recipe_engine/doc.proto`, or can emit gitiles-flavored
  Markdown (either on stdout or written to the repo).
  """
  
  def add_arguments(parser):
    doc_kinds = ('binarypb', 'jsonpb', 'textpb', 'gen', 'markdown')
    parser.add_argument(
        'recipe', nargs='?', help='Restrict documentation to this recipe')
    parser.add_argument(
        '--kind', default='jsonpb', choices=doc_kinds,
        help=(
          'Output this kind of documentation. `gen` will write the standard '
          'README.recipes.md file. All others output to stdout'))
  
    def _launch(args):
      from .cmd import main
      return main(args)
    parser.set_defaults(func=_launch)
  
new_contents: # Copyright 2019 The LUCI Authors. All rights reserved.
  # Use of this source code is governed under the Apache License, Version 2.0
  # that can be found in the LICENSE file.
  
  """Generate documentation from the recipes and modules in the current repo.
  
  This can output as a protobuf of various forms (JSON, Text or binary), using the
  `Doc` message in `recipe_engine/doc.proto`, or can emit gitiles-flavored
  Markdown (either on stdout or written to the repo).
  """
  
  def add_arguments(parser):
    parser.add_argument(
        'recipe', nargs='?', help='Restrict documentation to this recipe')
    parser.add_argument(
        '--kind', default='gen',
        choices=('gen', 'binarypb', 'jsonpb', 'textpb', 'markdown'),
        help=(
          'Output this kind of documentation. `gen` (the default) will write the'
          ' standard README.recipes.md file. All others output to stdout'))
  
    def _launch(args):
      from .cmd import main
      return main(args)
    parser.set_defaults(func=_launch)
  
subject: Change default to "gen".