update mnist data description (aws#2781)

Author: pymia

sagemaker_neo_compilation_jobs/tensorflow_distributed_mnist/tensorflow_distributed_mnist_neo.ipynb

@@ -228,7 +228,7 @@
  "output_path = \"/\".join(mnist_estimator.output_path.split(\"/\")[:-1])\n",
  "optimized_estimator = mnist_estimator.compile_model(\n",
  " target_instance_family=\"ml_c5\",\n",
- " input_shape={\"data\": [1, 784]}, # Batch size 1, 3 channels, 224x224 Images.\n",
+ " input_shape={\"data\": [1, 784]}, # Batch size 1, 1 channel, 28*28 image size.\n",
  " output_path=output_path,\n",
  " framework=\"tensorflow\",\n",
  " framework_version=\"1.15.3\",\n",