title: Shopify Script - Get a free X product when you spend Y amount
body: <p>I'm searching all over the internet for a solution, and I hope you guys help me with that.
  I want to do a shopify script that automatically add a specific free product if cart is over a specific amount (100$ for ex).
  All i've find online is X% discount if cart is over $Y, but I want to add an existing product.
  Is there a way to do it ?
  Thanks in advance </p>