net/http: add http.NotFoundHandler example

Change-Id: I6a69c7a5b829a967d75e1c79210a4906c0d8f505
Reviewed-on: https://go-review.googlesource.com/132276
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/http/example_test.go

@@ -173,3 +173,21 @@ func ExampleHandleFunc() {
 
 	log.Fatal(http.ListenAndServe(":8080", nil))
 }
+
+func newPeopleHandler() http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprintln(w, "This is the people handler.")
+	})
+}
+
+func ExampleNotFoundHandler() {
+	mux := http.NewServeMux()
+
+	// Create sample handler to returns 404
+	mux.Handle("/resources", http.NotFoundHandler())
+
+	// Create sample handler that returns 200
+	mux.Handle("/resources/people/", newPeopleHandler())
+
+	log.Fatal(http.ListenAndServe(":8080", mux))
+}