I've coded Org link support for EBDB, a contact management package,
where the :complete key looks like:

(lambda ()
  (format "ebdb:uuid/%s"
          (ebdb-record-uuid
           (ebdb-prompt-for-record
            (ebdb-records)))))

Which prompts for a record based on the contact name, then inserts the
contact's UUID as the link.

The problem is that Org then prompts for a link description. I'd like to
provide the contact name as a default description (the user has just
typed it in, after all), but haven't figured out how to do that.

Clearly `org-make-link-description-function' is meant to play this role,
and it would work perfectly, but I don't know to set it. I can't set it
globally, but also don't know how to let-bind it locally.

How am I supposed to use it?

Thanks,
Eric