documentation: fix docs in regards to transform_fn for mxnet

Author: imujjwal96

doc/using_mxnet.rst

@@ -689,7 +689,6 @@ Using ``transform_fn``
 ''''''''''''''''''''''
 
 If you would rather not structure your code around the three methods described above, you can instead define your own ``transform_fn`` to handle inference requests.
-This will override any implementation of ``input_fn``, ``predict_fn``, or ``output_fn``.
 ``transform_fn`` has the following signature:
 
 .. code:: python
@@ -704,6 +703,8 @@ The return object should be one of the following:
 - a tuple with two items: the response data and ``accept_type`` (the content type of the response data), or
 - a Flask response object: http://flask.pocoo.org/docs/1.0/api/#response-objects
 
+**Note:** We cannot use ``transform_fn`` implementation with ``input_fn``, ``predict_fn``, and/or ``output_fn``.
+
 You can find examples of hosting scripts using this structure in the example notebooks, such as the `mxnet_gluon_sentiment <https://github.com/awslabs/amazon-sagemaker-examples/blob/master/sagemaker-python-sdk/mxnet_gluon_sentiment/sentiment.py#L344-L387>`__ notebook.
 
 Working with existing model data and training jobs