Space Invaders playable game created with Python (and the pygame module)

1. To start the game, navigate to the command line and enter 'python3 alien_invasion.py'
2. Once the game GUI loads, start playing by either clicking Play in the middle of the screen, or press the 'P' button on your keyboard.
3. The objective of the game is to shoot down the alien ships. You, as the brave astronaut need to use your launchers by pressing the 'Spacebar' to destroy the alien fleets.
4. To quit, click on the red button at the top of the GUI, or press 'Q' on your keyboard.