Readme specifies that it handles .jpg images - Missing dependancy

[sam-wan]

Readme specifies that the script can handle .jpg images.

Error comes up from Matplotlib ValueError: Only know how to handle extensions: [u'png']; with Pillow installed matplotlib can handle more images

Installing Pillow, allowed me to rank .jpg images

Recommend: Add Pillow to the list of dependancies, or modify code to only look for .png's