Adding a web link to the email signup thank you page.

I have a signup page that I am using to sign up new people. I use a QR code so that people can input their information themselves. This saves a lot of time and mistakes. On the thank you page that comes up I would like to edit it to link to my constant contact website. How do I do that and if it is not available- why? This should be at least integrated for constant contact websites to direct new customers to. This seems to me to be a smart idea that should be available and it should be easy. The canned forms should be opened up a little to provide this.