tmpltohtml: put a DO NOT EDIT mark automatically in the output

R=r, rsc, r
CC=golang-dev
https://golang.org/cl/5469045

doc/effective_go.html

@@ -1,4 +1,9 @@
 <!-- Effective Go -->
+<!--
+  DO NOT EDIT: created by
+    tmpltohtml effective_go.tmpl
+-->
+
 
 <h2 id="introduction">Introduction</h2>
 

doc/effective_go.tmpl

@@ -1,4 +1,5 @@
 <!-- Effective Go -->
+{{donotedit}}
 
 <h2 id="introduction">Introduction</h2>
 

doc/go_tutorial.html

@@ -1,4 +1,10 @@
 <!-- A Tutorial for the Go Programming Language -->
+<!--
+  DO NOT EDIT: created by
+    tmpltohtml go_tutorial.tmpl
+-->
+
+
 <h2>Introduction</h2>
 <p>
 This document is a tutorial introduction to the basics of the Go programming

doc/go_tutorial.tmpl

@@ -1,4 +1,6 @@
 <!-- A Tutorial for the Go Programming Language -->
+{{donotedit}}
+
 <h2>Introduction</h2>
 <p>
 This document is a tutorial introduction to the basics of the Go programming

doc/tmpltohtml.go

@@ -35,6 +35,11 @@ func Usage() {
 	os.Exit(2)
 }
 
+var templateFuncs = template.FuncMap{
+	"code":      code,
+	"donotedit": donotedit,
+}
+
 func main() {
 	flag.Usage = Usage
 	flag.Parse()
@@ -44,7 +49,7 @@ func main() {
 
 	// Read and parse the input.
 	name := flag.Args()[0]
-	tmpl := template.New(name).Funcs(template.FuncMap{"code": code})
+	tmpl := template.New(name).Funcs(templateFuncs)
 	if _, err := tmpl.ParseFiles(name); err != nil {
 		log.Fatal(err)
 	}
@@ -80,6 +85,11 @@ func format(arg interface{}) string {
 	return ""
 }
 
+func donotedit() string {
+	// No editing please.
+	return fmt.Sprintf("<!--\n  DO NOT EDIT: created by\n    tmpltohtml %s\n-->\n", flag.Args()[0])
+}
+
 func code(file string, arg ...interface{}) (string, error) {
 	text := contents(file)
 	var command string