CIP: Add version suffix -cip28

Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
diff --git a/localversion-cip b/localversion-cip
new file mode 100644
index 0000000..72a88e3
--- /dev/null
+++ b/localversion-cip
@@ -0,0 +1 @@
+-cip28