Add strategy design pattern example

Author: gjbex

source-code/design-patters/README.md

@@ -8,5 +8,7 @@ Code to illustrate some design patterns in Python.
    can be used to change the behaviour of objects.
 1. `factory_design_pattern.ipynb`: notebook illustrating how a factory class
    can be used to conveniently construct many objects with the same properties.
-  * `finite-state-parser`: illustration of object-oriented data
+1. `finite-state-parser`: illustration of object-oriented data
     representation and the state pattern.
+1. `strategy_design_pattern.ipynb`: notebook illustrating how a strategy
+   design pattern can simplify simulations.