[gtk+] accellabel: Fix code snippet

[Timm Bäder <baedert src gnome org>]

commit da3d2593b210ee3ceff0d3522a256cd04188fde7
Author: Timm Bäder <mail baedert org>
Date:   Wed Oct 11 12:56:42 2017 +0200

    accellabel: Fix code snippet

 gtk/gtkaccellabel.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/gtk/gtkaccellabel.c b/gtk/gtkaccellabel.c
index 0521ffb..38b4963 100644
--- a/gtk/gtkaccellabel.c
+++ b/gtk/gtkaccellabel.c
@@ -76,6 +76,8 @@
  * ## Creating a simple menu item with an accelerator key.
  *
  * |[<!-- language="C" -->
+ *   GtkWidget *window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
+ *   GtkWidget *menu = gtk_menu_new ();
  *   GtkWidget *save_item;
  *   GtkAccelGroup *accel_group;
  *