It's here: http://demigod.wikia.com/wiki/Guides
Since I just started the section it's a bit empty right now (only containing two and a half guides), but I'm sure it will be populated soon.
Moreover, all guides can (and should) be linked to the respective Demigod. See the page of General Oak to get a feel for how neat guides can be incorporated in the wiki.
Hope to see your guides there!