[gtk+] Add a release note about level bar changes

[Matthias Clasen <matthiasc src gnome org>]

commit e32da776ce23a32cc95ab033e4b2cb3b1253b79a
Author: Matthias Clasen <mclasen redhat com>
Date:   Mon Feb 15 22:43:56 2016 -0500

    Add a release note about level bar changes

 README.in |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)
---
diff --git a/README.in b/README.in
index 5f3ce4e..a7863bd 100644
--- a/README.in
+++ b/README.in
@@ -102,6 +102,11 @@ Release notes for 3.18
   GtkCellRendererText is no longer ignored. If you don't want your
   text to be translucent, use opaque colors.
 
+* The way in which GtkLevelBar determines the offset to apply was
+  a bit inconsistent in the past; this has been fixed. Applications
+  that are using custom offsets should double-check that their
+  levels look as expected.
+
 Release notes for 3.16
 ======================