syscall: document that documentation is platform specific
syscall: document that documentation is platform specific

Fixes issue 4051

R=golang-dev, minux.ma, rsc
CC=golang-dev
https://codereview.appspot.com/6943063

Committer: Shenghou Ma <b563c57947dc20eb81988e3e3c22786764c14ca8@gmail.com>

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang