[gtk+] scrolledwindow: Fix code sample compilation

[Timm Bäder <baedert src gnome org>]

commit 4a999cbd1f5b1ff1dc9df7ba273de6378c5298d7
Author: Timm Bäder <mail baedert org>
Date:   Wed Jan 3 13:51:03 2018 +0100

    scrolledwindow: Fix code sample compilation

 gtk/gtkscrolledwindow.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)
---
diff --git a/gtk/gtkscrolledwindow.c b/gtk/gtkscrolledwindow.c
index ece2bb2..4f9933e 100644
--- a/gtk/gtkscrolledwindow.c
+++ b/gtk/gtkscrolledwindow.c
@@ -68,8 +68,13 @@
  *
  * If gtk_container_add() has added a #GtkViewport for you, you can remove
  * both your added child widget from the #GtkViewport, and the #GtkViewport
- * from the GtkScrolledWindow, with either of these calls:
+ * from the GtkScrolledWindow, like this:
  * |[<!-- language="C" -->
+ * GtkWidget *scrolled_window = gtk_scrolled_window_new (NULL, NULL);
+ * GtkWidget *child_widget = gtk_button_new ();
+ *
+ * // GtkButton is not a GtkScrollable, so GtkScrolledWindow will automatically
+ * // add a GtkViewport.
  * gtk_container_remove (GTK_CONTAINER (scrolled_window),
  *                       child_widget);
  * // or