Add help link to three rather important pages
- Specialpages is a useful hub, but not so visited. The help page is currently not that good, but is not controversial either.
- Preferences should obviously be better, but may be better than nothing. Some explanations and links there are definitely useful.
- Categories don't worry much and there's no doubt they require more education to be really understandable and useful for users. They are however sort of content pages, if users start thinking they can get help about the contents of the categories of specific wikis we'll need to remove the link.