runtime, unicode: use consistent banner for generated code

Per golang.org/s/generatedcode

Updates #nnn

Change-Id: Ia7513ef6bd26c20b62b57b29f7770684a315d389
Reviewed-on: https://go-review.googlesource.com/45470
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Matt Layher <mdlayher@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/src/unicode/maketables.go b/src/unicode/maketables.go
index fdfcde4..e52d9c2 100644
--- a/src/unicode/maketables.go
+++ b/src/unicode/maketables.go
@@ -443,9 +443,9 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Generated by running
+// Code generated by maketables; DO NOT EDIT.
+// To regenerate, run:
 //	maketables --tables=%s --data=%s --casefolding=%s
-// DO NOT EDIT
 
 package unicode