It would help to have this clarified and intuitive on the login page at: https://www.dokuwiki.org/dokuwiki?do=login
A link to the forum registration page would suffice. It would also be beneficial to link to this forum post for an explanation.
Maybe try a "Register" button/link and "Explain registration..." link.
When making a number of documentation additions and changes, I could not find any Registration mechanism, so I made the changes without an account. When I found that it would be beneficial to be able to receive notifications on one of the pages I was editing, I went on a further search for how to get an account. It took me 2 days, going onto IRC getting no response, and eventually combing the forums to find this post.