[glibmm] Add a comment

[Murray Cumming <murrayc src gnome org>]

commit 4c4fef8a57a0532d390a1542720aa9f2cc47568f
Author: Murray Cumming <murrayc murrayc com>
Date:   Wed Apr 3 23:39:29 2013 +0200

    Add a comment

 glib/glibmm/class.cc |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/glib/glibmm/class.cc b/glib/glibmm/class.cc
index 913b17d..5cb9130 100644
--- a/glib/glibmm/class.cc
+++ b/glib/glibmm/class.cc
@@ -59,7 +59,7 @@ void Class::register_derived_type(GType base_type, GTypeModule* module)
     class_size,
     0, // base_init
     0, // base_finalize
-    class_init_func_,
+    class_init_func_, //Set by the caller ( *_Class::init() ).
     0, // class_finalize
     0, // class_data
     instance_size,