[gtk+] Add a release note about background rendering

[Matthias Clasen <matthiasc src gnome org>]

commit 04b58bcf3e87e2495f810449d717e86a0f0a3171
Author: Matthias Clasen <mclasen redhat com>
Date:   Mon Feb 3 16:49:15 2014 -0500

    Add a release note about background rendering

 README.in |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)
---
diff --git a/README.in b/README.in
index e5d4249..6c109db 100644
--- a/README.in
+++ b/README.in
@@ -92,6 +92,11 @@ Release notes for 3.12
   it used to inconsistently scroll with the buffer but then go
   reposition to a window-relative position on redraw.
 
+* A number of container widgets have been made more compliant with
+  the uniform CSS rendering model by making them render backgrounds
+  and borders. This may require some adjustments in applications that
+  were making assumptions about containers never rendering backgrounds.
+
 Release notes for 3.10
 ======================