Add HTML or script in course? I thought I saw this somewhere

I would like to be able to add some html to a course unit, I thought I saw somewhere how to do it but I can't find it anymore?
When I paste my script
<!-- start HangATag script -->
<div data-id="361" class="__hngtg">View blog post for supplies</div>
<script src="//www.hangatag.com/js/a.js"></script>
<!-- end HangATag script -->
I just see lines...