X16 documentation for YM2151 programming

[ZeroByte]

Just in case anyone's been looking for information on how to write code for the YM2151, the Offical documentation now has a register reference in the style of the other documentation sections, and also includes a short "getting started" tutorial on the task of communicating with the chip. It doesn't go into FM instrument design theory, as that's beyond the scope of such a document.

https://github.com/commanderx16/x16-docs/blob/master/X16 Reference - 09 - Sound Programming.md