Sign-up with an extra field

Hi! We have a private forum with only an only invite access. We want to eventually allow external users to join our community by signing up with the admins pre-approval.

However, we would like to add an extra field only in the sign-up form for the new users to provide a small description about themselves and why want to join our community. Any ideas about how to do that ?

Thanks in advance! Discourse rocks :v:

I think it’s Settings - Customise - User Fields.