[gtk/ebassi/gidocgen] printdialog: Add an example image

[Matthias Clasen <matthiasc src gnome org>]

commit f701b7b15abe70704b8fdd2d22c10af265d31350
Author: Matthias Clasen <mclasen redhat com>
Date:   Sat Feb 27 18:22:52 2021 -0500

    printdialog: Add an example image

 gtk/gtkprintunixdialog.c | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/gtk/gtkprintunixdialog.c b/gtk/gtkprintunixdialog.c
index 4a1ce1e81a..66cfc47fb1 100644
--- a/gtk/gtkprintunixdialog.c
+++ b/gtk/gtkprintunixdialog.c
@@ -60,6 +60,8 @@
  * `GtkPrintUnixDialog` implements a print dialog for platforms
  * which don’t provide a native print dialog, like Unix.
  *
+ * ![An example GtkPrintUnixDialog](printdialog.png)
+ *
  * It can be used very much like any other GTK dialog, at the cost of
  * the portability offered by the high-level printing API with
  * [class@Gtk.PrintOperation].