add installation note

Author: brean

README.md

@@ -15,6 +15,15 @@ Dijkstra and A* take the weight of the fields on the map into account.
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+Installation
+------------
+This library is provided by pypi, so you can just install the current stable version using pip:
+```
+pip install pathfinding
+```
+
+see https://pypi.org/project/pathfinding/
+
 usage example
 -------------
 A simple usage example to find a path using A*.