Updated README, Fixed class parameter

[Meeeee6623]

Updated the README files for MxNet and TensorFlow for Image Classification. The Quick Start guides were missing a line crucial to data preperation: wget -qO- https://raw.githubusercontent.com/soumith/imagenetloader.torch/master/valprep.sh | bash This line seperates the ImageNet data into classes, and is needed for preprocessing with the given script for TensorFlow.

In addition, for MxNet, the num-classes parameter was passed through from the command line, but never updated in models.py.