There's a link and some stupid GI cash you get. But the amount you get is worthless...you have to refer, like, 20 people to get free supporter or something.

Actually, you'd have to refer 140 people.

However...

"Also remember, that if any of the users referred by you will like the game and will decide to support the project by purchasing the supporter account, you will be immediately rewarded by 1 month of free supporter account (if your referral supports the game by purchasing a 1 year supporter account), or 7 days of free supporter account (if your referral supports the game by purchasing a 3 months supporter account)."

You can find your referral link under settings on your home page.