dl: add go1.20

Change-Id: Iad4848e80003e8b1b5d17fd9a3131aa7b3f0129c
Reviewed-on: https://go-review.googlesource.com/c/dl/+/464495
Auto-Submit: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Gopher Robot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

go1.20/main.go

diff --git a/go1.20/main.go b/go1.20/main.go
new file mode 100644
index 0000000..824716d
--- /dev/null
+++ b/go1.20/main.go
@@ -0,0 +1,24 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// The go1.20 command runs the go command from Go 1.20.
+//
+// To install, run:
+//
+//	$ go install golang.org/dl/go1.20@latest
+//	$ go1.20 download
+//
+// And then use the go1.20 command as if it were your normal go
+// command.
+//
+// See the release notes at https://go.dev/doc/go1.20.
+//
+// File bugs at https://go.dev/issue/new.
+package main
+
+import "golang.org/dl/internal/version"
+
+func main() {
+	version.Run("go1.20")
+}