The Registration Forms editor allows you to add custom HTML to your forms.
Underneath the fields in the left hand section of the form editor, is a button to ‘Add HTML’.
When clicked a modal appears with a rich text editor where you can add HTML that will appear in the form.
When saved, the HTML is added underneath the fields on the form. However, these HTML fields can be dragged around and reordered between the existing fields.
The HTML is then displayed on the frontend form:
The HTML fields even support adding shortcodes that will be rendered on the form.