If you put all your html files in the root, you have a web application, without WEB-INF. Yes, it sucks but it works. This hint is focusing on the "must have" part. A web application may have a special WEB-INF directory, but it's not mandatory. Without it, you'll have a working crappy web application
By the way, the hints you are looking at are maintained by a rancher (Jothi, where are you ?), but are not reviewed by anybody, so be careful.