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Yeah, I agree that is a good thing to add to your faq. But, the ideal way to handle this is either a text message of a link to help on this issue on the registration page.
Someone new comes to the site, usually, they will either like the content and want to join. Or they won't. I doubt any will automatically read the faq to learn how to join a site.
My site being related to computer security information, have a lot of visitors with cookies disabled.
And I too get a lot of hits on the registration page, but few actual joins.