indeed that would be also a very good solution and idea. Also for other things/facts you would like to look up easily (for sure there will be some questions about mechanics, Background stories (of Major characters/npc´s, history, etc.)
if you could do both (mouseover and ingame Manual), it would be perfect!
If for example "burning" is scaled with skills/Levels it could show you the effectively damage per round - i think it will be not an expensive programming-part, right ?
btw i like the "tutorial" so far, it´s not you explain every key but the main things - for me it is perfect - it is not all at the very first beginning, you have to spam through

you can starting to explore and step by step you learn... thats perfect from my point of view