doc: update README file

Change-Id: I97ae0f692d8237f4f410298740371991c18caaf8
Reviewed-on: https://go-review.googlesource.com/1341
Reviewed-by: Andrew Gerrand <adg@golang.org>

README

diff --git a/README b/README
index bc954b0..425ffc3 100644
--- a/README
+++ b/README
@@ -1,16 +1 @@
-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.
-
-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).
+This subrepository holds benchmarks used by the perf dashboard.