Update design_prototype_decent.py

Test // | Game | Help | Quit
Welcome to the application
>>> quit
Test // | Main
Do you really want to Exit? (y/n)
>>> n
Test // | Game | Help | Quit
Welcome to the application
>>> help
Test // | Main
This is how you use this application
>>> main
Test // | Game | Help | Quit
Welcome to the application
>>> game
Test // | Main | Help
Let us play this game
>>> help
Test // | Game
This is how you use this application
>>> game
Test // | Main | Help
Let us play this game
>>> main
Test // | Game | Help | Quit
Welcome to the application
>>> quit
Test // | Main
Do you really want to Exit? (y/n)
>>> y