Implemented collision detection
When an alien is destroyed, add a point
Added a GameOver scene
Import SpriteKit
Added the init constructor for the GameOver scene
Selecting the message to show in the GameOver scene
Added configuration for the label
Add label to the screen
Add the background color
Added actions for the GameOver scene
Added action for the alien: transition to the game over scene if the alien went offscreen
Checking if you won
Fixed typo
Added README for SpaceInvader
Updated main README.md