Follow these steps:
1. Create a Hatchbuck form with just 1 field - email address. Add a header that says something like "Enter your Friend's Email"
2. Add an action on the form to 'send an email' and choose your template
3. Once the form is saved, grab the url from the 'embed and integrate' section
4. Go to your email template and add text at the top that reads "Forward to a Friend" and hyperlink your text to the forms url