[libgd] README: add GNOME Boxes commit link and hint

[Marc-Andre Lureau <malureau src gnome org>]

commit bd1887878a09f8b035ab19beed55422d6441046f
Author: Marc-Andrà Lureau <marcandre lureau gmail com>
Date:   Mon Aug 20 21:13:11 2012 +0200

    README: add GNOME Boxes commit link and hint

 README |   11 ++++++++++-
 1 files changed, 10 insertions(+), 1 deletions(-)
---
diff --git a/README b/README
index 83be2aa..d0088e1 100644
--- a/README
+++ b/README
@@ -51,7 +51,6 @@ approach has the following advantages:
 - the libgd options should help you to configure a library to suit
   your needs, taking care of some of autofoo stuff for you
 
-
 Usage
 =====
 
@@ -76,6 +75,16 @@ In order to use libgd, an application using autotools needs to:
     - link with $(top_builddir)/libgd/libgd.la, and include
       <libgd/gd.h> (adjust your AM_CPPFLAGS as necessary)
 
+You may be interested to look at the commit switching GNOME Boxes from
+private libgd usage to the libgd submodule:
+
+http://git.gnome.org/browse/gnome-boxes/commit/?id=395652458d8b311a25ecb27cc42287602a122b1f
+
+Note for example that the submodule url is "../libgd", which is a
+better alternative for projects hosted on git.gnome.org. It will allow
+the submodule update to reuse the address and the credentials given to
+the toplevel project.
+
 LIBGD_INIT options
 ==================