Append the new dataset file to the __init__.py.

def add_the_init(root_dir, data):
  """Append the new dataset file to the __init__.py."""
  init_file = os.path.join(root_dir, '{dataset_type}', '__init__.py')
  context = (
      'from tensorflow_datasets.{dataset_type}.{dataset_name} import '
      '{dataset_cls}  # {TODO} Sort alphabetically\n'
  )
  with gfile.GFile(init_file.format(**data), 'a') as f:
    f.write(context.format(**data))