The title is a bit over dramatic but, per the title, if you could contribute with one piece of knowledge to a book that every single individual should learn from in order to kickstart a civilization, what would be yours?
My personal choice would be the process of soap making, from scratch.
The meaning of life is very very simple, love yourself and those around you as much as possible and have as much fun as you can. If it doesn’t hurt anyone or anything and you have fun doing it, do it a lot. When you genuinely love everyone around you, living becomes a lot easier and the meaning of life becomes simple.