[glib] Note G_MESSAGES_DEBUG in README

[Ryan Lortie <ryanl src gnome org>]

commit 6784468625a77b3daa1247f2199bc11714cb4eca
Author: Ryan Lortie <desrt desrt ca>
Date:   Thu Jan 19 22:13:51 2012 -0500

    Note G_MESSAGES_DEBUG in README

 README.in |   10 ++++++++++
 1 files changed, 10 insertions(+), 0 deletions(-)
---
diff --git a/README.in b/README.in
index 8ae830b..6d53029 100644
--- a/README.in
+++ b/README.in
@@ -63,6 +63,16 @@ Notes about GLib 2.32
   on gthread-2.0.pc (if you care about compatibility with older GLib
   versions) or to stop calling g_thread_init().
 
+* g_debug() output is no longer enabled by default.  It can be enabled
+  on a per-domain basis with the G_MESSAGES_DEBUG environment variable
+  like
+
+    G_MESSAGES_DEBUG=domain1,domain2
+
+  or
+
+    G_MESSAGE_DEBUG=all
+
 Notes about GLib 2.30
 =====================