If what you're worried about is breaking immersion by explaining the combat, then my simple suggestion would be to use the books more. I liked the books a lot and felt that they were very effective ways of teaching basic mechanics that I could both go back too, while also feeling natrual. Like, there's nothing odd about a book listing different sciences, like phobias or different chemical combinations.
So, I would simply suggest adding a book that's a 'guarenteed drop', since there are things that seem to do spawn with each new playthrough somewhere in the first area, to reward exploration and since you've probably fought a guard by then, it kinda gives you this "ooh, so that's how you do it, I get it" feeling.
As for the contents, just make it about some prison guard captain or something listing some basic combat tips directed to his guards, like "Always go for the limbs first, to make it easier to hit the head", and or whatever. Such tips, I think, would nudge the player toward learning some of the basic mechanics, while also remaining natrual and not giving away too much.