I hadn't seen this post anywhere but wanted to add it incase another user wanted to know how to do it. I wanted to add a link in the footer to a privacy notice so participants can see how their data is going to be used. It was pretty straight forward:
Open Survey
Open Look and Feel
Open General
Copy the following into the Footer portion:
<span style="font-size:11px;">By clicking Next, the data you share will be handled in accordance with the <a href="https://your-link.com" target="_blank"> -What you want your link to say-</span></a>
Bolded portion above can be amended to reflect your message, your link and what the link says.