message: update docs for onnx.save_model
diff: @@ -201,13 +201,18 @@ def save_model(
  Arguments:
  proto: should be a in-memory ModelProto
  f: can be a file-like object (has "write" function) or a string containing a file name format for future use
  - all_tensors_to_one_file: If true, save all tensors to one external file specified by location.
  + save_as_external_data: If true, save tensors to external file(s).
  + all_tensors_to_one_file: Effective only if save_as_external_data is True.
  + If true, save all tensors to one external file specified by location.
  If false, save each tensor to a file named with the tensor name.
  - location: specify the external file that all tensors to save to.
  + location: Effective only if save_as_external_data is true.
  + Specify the external file that all tensors to save to.
  If not specified, will use the model name.
  - size_threshold: Threshold for size of data. Only when tensor's data is >= the size_threshold it will be converted
  + size_threshold: Effective only if save_as_external_data is True.
  + Threshold for size of data. Only when tensor's data is >= the size_threshold it will be converted
  to external data. To convert every tensor with raw data to external data set size_threshold=0.
  - convert_attribute: If true, convert all tensors to external data
  + convert_attribute: Effective only if save_as_external_data is True.
  + If true, convert all tensors to external data
  If false, convert only non-attribute tensors to external data
  """
  if isinstance(proto, bytes):
  