[gtk+/gtk-3-22] HeaderBar: Explain use in conjunction w/ GtkWindow

[Daniel Boles <dboles src gnome org>]

commit b5e4a9d716c9146ac1ef398684a090f0a4743fc7
Author: Daniel Boles <dboles src gnome org>
Date:   Fri Jan 12 22:56:11 2018 +0000

    HeaderBar: Explain use in conjunction w/ GtkWindow
    
    After hinting how good GtkHeaderBar is for GtkWindow, let’s link to
    the latter and indicate how users can make the two work together.

 gtk/gtkheaderbar.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/gtk/gtkheaderbar.c b/gtk/gtkheaderbar.c
index ae85993..a731cca 100644
--- a/gtk/gtkheaderbar.c
+++ b/gtk/gtkheaderbar.c
@@ -51,6 +51,10 @@
  *
  * GtkHeaderBar can add typical window frame controls, such as minimize,
  * maximize and close buttons, or the window icon.
+ *
+ * For these reasons, GtkHeaderBar is the natural choice for use as the custom
+ * titlebar widget of a #GtkWindow (see gtk_window_set_titlebar()), as it gives
+ * features typical of titlebars while allowing the addition of child widgets.
  */
 
 #define DEFAULT_SPACING 6