go.empty: restore the README

I edited the wrong README when cloning the empty repo to create the tools one.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/9486043

README

-This subrepository holds the source for various packages and tools that support
-the Go programming language.
+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.
 
-Although at least some of the tools themselves will be included in binary Go distributions,
-the packages from which they are built are of little interest to most Go programmers.
+Then execute:
+	go get code.google.com/p/go.newrepo
+	cd $(go list -e -f '{{.Dir}}' code.google.com/p/go.newrepo)
 
-To submit changes to this repository, see http://golang.org/doc/contribute.html.
+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).