I agree. I use MySQL and its site since 2001 I think, and never knew of that "user guide", or suspected that contributes on any part of the wiki are welcome.
But, I think that also AskMonty KB doesn't make it "immediatly clear":
* In the home page and in the sidebar, I can see no link like "How to contribute" ("about AM KB" is not in evidence, and it's not clear it's written for contributors)
* Categories don't have an "add page" link, nor articles have "edit" button visible to anyone (they could be disabled for non-registered users)

Also, MySQL docs seem to strictly follow some (good) guidelines. AM KB doesn't: pages are written with different styles, some categories seem to be duplicated, and many articles are not listed in some related categories. A lack of guidelines does not encourage people who want to contrib with quality content.

I think that this is a problem for translations, too. I'm trying to write quality translations into italian, but I'm following my own style. What will happen when more italian users will add their own contributes? All italian translation projects I know have public guidelines, and lack of rules/help may lead to bad translations, in my opinion.

Cheers
Federico