Unless they are really interested in knives as a hobby, I'd keep it simple. Just some brief notes about storage (light coat of pretty much any mineral oil, keep them out of the sheath if they are made out of leather, etc), tell them to use a soft surface to cut on (cutting board or something like that) and basic sharpening (there are lots of good pictures on-line you can use). Also, include a little strop, it costs next to nothing and does wonders to keep an edge sharp while being easier to master than a sharpening stone.
I used to sell knives at a store and most people wouldn't read anything longer than a page. Those who were interested in learning more would ask, order books or look for tutorials on-line. So my advice is to keep it simple, if people want more information they'll ask.