more instructive NEWS

--- a/NEWS	Thu Mar 22 17:52:50 2012 +0000
+++ b/NEWS	Thu Mar 22 18:37:20 2012 +0100
@@ -120,6 +120,9 @@
 
 Generalized theorems INF_INT_eq, INF_INT_eq2, SUP_UN_eq, SUP_UN_eq2.
 
+See theory "Relation" for examples for making use of pred/set conversions
+by means of attributes "to_set" and "to_pred".
+
 INCOMPATIBILITY.
 
 * Consolidated various theorem names relating to Finite_Set.fold