You might have better luck over at the Xilinx forums. However, in the mean time, you can take a look at these links. I see what you are after and to be honest, I was not following that file, so I am not sure what replaced it. A lot of documents got changed around when Vitis came out. Looking at the versions of UG981, looks like around 2014 was the last version - which to me lines up right around when Xilinx started to line up better with the "normal" Yocto flow. It seems to be that the last link in my list below is close - but a LOT of the Xilinx documentation around this kind of stuff has gone HTML and you might find what you want on the second link. I think by Xilinx mostly complying to Yocto flow, any normal Yocto documentation works related to normal PetaLinux application development. That said, the older docs. might be a good starting point anyway.
