That is an interesting idea. I have seen this well executed in the documentation of SPICE. The docs for the individual functions, e.g. here, link back to more in-depth “required reading” articles, e.g. here.
Concerning the Julia manual, I think it shows that it has grown organically over the years (which is not a bad thing in itself). In my opinion, it is also much too dense (again not a bad thing in itself) to serve as an entry point for a beginner. What’s missing is something like the Swift Tour which gives a good feel for the language and is a lot less scary.