How to add a multi-line text field to a Discourse Community signup page?

I would like to add a multi-line text field to my Discourse community’s signup page, but I am not sure how. Am I able to edit the source code to do this, add a file to the source code, or use a plugin that enables this? Either way, I am unsure how to accomplish this task.

I tried using the default settings first and was only presented with single-line text field, confirmation, drop-down, and multi-select field options.