[dev.go2go] README: document that this branch is no longer maintained

For golang/go#46346

Change-Id: Iab050557efb96217477072eca42966662485b6b1
Reviewed-on: https://go-review.googlesource.com/c/go/+/322192
Trust: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
diff --git a/README.go2go.md b/README.go2go.md
index 6930889..1ff8c98 100644
--- a/README.go2go.md
+++ b/README.go2go.md
@@ -1,5 +1,15 @@
 # dev.go2go branch
+This branch provides an experimental go2go tool for testing the use of
+the generics design draft.
+This branch was published in 2020 and is no longer being maintained.
+The [generics
+has [been accepted](https://golang.org/issue/43651) and development is
+now focused on implementing the proposal in the ordinary Go tools.
+## Original README
 This branch contains a type checker and a translation tool for
 experimentation with generics in Go.
 This implements the [generics design draft](https://go.googlesource.com/proposal/+/refs/heads/master/design/go2draft-type-parameters.md).
diff --git a/src/cmd/go2go/doc.go b/src/cmd/go2go/doc.go
index 059b91b..1d8cf05 100644
--- a/src/cmd/go2go/doc.go
+++ b/src/cmd/go2go/doc.go
@@ -5,6 +5,9 @@
 // go2go is a command for trying out generic Go code.
 // It supports a small number of commands similar to cmd/go.
+// This tool was intended for experimental use during the development
+// of the generics proposal, and is no longer maintained.
 // Usage:
 //	go2go [options] <command> [go2go flags] [arguments]