[gtk+] level bar: Document buildable syntax

[Matthias Clasen <matthiasc src gnome org>]

commit c3c01d8cbcac8515ce8bd16ceef661dbe9920b1f
Author: Matthias Clasen <mclasen redhat com>
Date:   Sun Feb 7 11:28:08 2016 +0100

    level bar: Document buildable syntax

 gtk/gtklevelbar.c |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletions(-)
---
diff --git a/gtk/gtklevelbar.c b/gtk/gtklevelbar.c
index aed5920..46684cd 100644
--- a/gtk/gtklevelbar.c
+++ b/gtk/gtklevelbar.c
@@ -87,7 +87,13 @@
  * set the minimum value to 0 and the maximum value to 5 after changing the indicator
  * mode to discrete.
  *
- * Since: 3.6
+ * GtkLevelBar was introduced in GTK+ 3.6.
+ *
+ * # GtkLevelBar as GtkBuildable
+ *
+ * The GtkLevelBar implementation of the GtkBuildable interface supports a
+ * custom <offsets> element, which can contain any number of <offset> elements,
+ * each of which must have name and value attributes.
  *
  * # CSS nodes
  *