Adds instruction to start
Adds a lot of things!! Game almost done!

Adds ball movement function
Adds collision detection with walls
Adds collision detection with players (NEED TO BE FIXED!)
Adds ball drawing function
Adds score management
Adds score drawing function to show the scores
Adds system to restart playing when one of the players scores
Adds system to don't start when web page loads (need to press enter)
Adds system to full restart to play another game (NEED TO BE FIXED!)
Adds better game loop and main functions structure