[gnome-builder] gtk: add comment on gtk helper

[Christian Hergert <chergert src gnome org>]

commit 0d121f28fccf419775cb320fa74b45be7325f0a6
Author: Christian Hergert <christian hergert me>
Date:   Sat Dec 20 01:55:22 2014 -0800

    gtk: add comment on gtk helper

 src/util/gb-gtk.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)
---
diff --git a/src/util/gb-gtk.c b/src/util/gb-gtk.c
index 287eec1..10e7017 100644
--- a/src/util/gb-gtk.c
+++ b/src/util/gb-gtk.c
@@ -29,6 +29,11 @@ struct ScrollState
   gdouble      yalign;
 };
 
+/*
+ * This function is like gtk_text_buffer_get_iter_at_line_offset() except that
+ * the line offset does not need to exist. It will work forward as far as
+ * possible on that line.
+ */
 void
 gb_gtk_text_buffer_get_iter_at_line_and_offset (GtkTextBuffer *buffer,
                                                 GtkTextIter   *iter,