[gtk+/wip/matthiasc/gadget] Expand gadget docs a bit

[Matthias Clasen <matthiasc src gnome org>]

commit 55ed9abdd3330833ef8e358258ccf08fa367c4fc
Author: Matthias Clasen <mclasen redhat com>
Date:   Thu Dec 10 23:12:28 2015 -0500

    Expand gadget docs a bit
    
    Point out that the style context needs to be manually
    saved to the gadget's CSS node when necessary.

 gtk/gtkcsscustomgadget.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)
---
diff --git a/gtk/gtkcsscustomgadget.c b/gtk/gtkcsscustomgadget.c
index a95dac0..1e6962a 100644
--- a/gtk/gtkcsscustomgadget.c
+++ b/gtk/gtkcsscustomgadget.c
@@ -27,7 +27,10 @@
  * GtkCssCustomGadget is a subclass that lets widgets customize size
  * requests, size allocation and drawing of gadgets. The gadget is passed
  * to the callbacks as the first argument, and you can use gtk_css_gadget_get_owner()
- * to obtain the widget.
+ * to obtain the widget. Note that the widgets style context is not saved,
+ * so if you want to query style properties or call gtk_render functions which
+ * take the style context as an argument, you should use
+ * gtk_style_context_save_to_node to make the gadget's CSS node take effect.
  *
  * The callbacks are
  *