Use left and right arrow keys to move ship, space to fire!
Graphical assets were taken from Ray Wenderlich's article on how to build Space Invaders in Swift. Worth a read if you want to compare Scratch development with how we build iOS apps! https://www.raywenderlich.com/2642-how-to-make-a-game-like-space-invaders-with-sprite-kit-tutorial-part-1
