Update README.md

README.md

-'''About'''
+# About
 Generate an artistic image from given content image and style image
 
-'''Pre-requisite'''
-python
+## Pre-requisite
+python3
 tensorflow
 keras
 
-'''How to use'''
+## How to use
 All images sizes should be 400x300
 Put your content image in images/content.jpg file
 Put your style image in images/style.jpg file