[gtk+] docs: add missing info for gtk_widget_get_style_context()

[Matthias Clasen <matthiasc src gnome org>]

commit 3432587f890e58584907776d45bb54b82cf25f89
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Sun Jul 24 13:16:31 2016 +0200

    docs: add missing info for gtk_widget_get_style_context()
    
    It is important to know whether the returned object can or cannot
    change, for a certain widget. For example to connect to the
    GtkStyleContext::changed signal.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=769047

 gtk/gtkwidget.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/gtk/gtkwidget.c b/gtk/gtkwidget.c
index a8ad232..52a9995 100644
--- a/gtk/gtkwidget.c
+++ b/gtk/gtkwidget.c
@@ -16542,7 +16542,8 @@ _gtk_widget_peek_style_context (GtkWidget *widget)
  * gtk_widget_get_style_context:
  * @widget: a #GtkWidget
  *
- * Returns the style context associated to @widget.
+ * Returns the style context associated to @widget. The returned object is
+ * guaranteed to be the same for the lifetime of @widget.
  *
  * Returns: (transfer none): a #GtkStyleContext. This memory is owned by @widget and
  *          must not be freed.