go.sys: create new repository

See http://golang.org/s/go1.4-syscall for background.

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/123130043

README

-This is an empty Go subrepository.  To create a new subrepository,
-visit http://code.google.com/p/go/adminSource and under repositories,
-type the new name, check [x] Clone contents and select [empty] as
-the one you want to clone.
+This repository holds supplemental Go packages for low-level interactions with the operating system.
 
-Then execute:
-	go get code.google.com/p/go.newrepo
-	cd $(go list -e -f '{{.Dir}}' code.google.com/p/go.newrepo)
-
-The go get will complain about not finding source code, but it will
-successfully check out the repository.
-
-Edit the README (this file) to describe the new subrepository, and then
-use the usual hg change, mail, submit to send in the change.
-You will need to follow http://golang.org/doc/contribute.html#Code_review
-to enable the Code Review extension (pointing into your Go root).
+To submit changes to this repository, see http://golang.org/doc/contribute.html.