The wiki login page should have the help text, it's not enough that it's on one almost-random page. I tried to find a way to login, but all I could find was

a) The "Customer login" link which got me to JIRA (this was very confusing, since even after registering and logging in to JIRA I still couldn't edit the wiki), and
b) a Log in button on the bottom of the page, which wouldn't take the password that I created using the only sign up form I could find from the wiki.