Valve began rolling out a new Steam beta feature today: game guides. The aim is exactly what you're thinking it is.
Anyone can make a guide, and they'll be accessible on a game's "hub" page, as you can see above. You can upload images, embed YouTube vidos and rope in friends on your friends list to help out.
The fact it has images and video, is tapping into a passionate community and will be accessible form within Steam make this sound very cool. Hopefully it's not too long before people get cracking on them.