Add license badge

Author: brean

README.md

@@ -14,6 +14,7 @@ Dijkstra and A* take the weight of the fields on the map into account.
 
 [![Build Status](https://travis-ci.org/brean/python-pathfinding.svg?branch=master)](https://travis-ci.org/brean/python-pathfinding)
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+![MIT License](https://img.shields.io/github/license/brean/python-pathfinding)
 
 Installation
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