Add note about assignment to __debug__ being an error.
diff --git a/Misc/NEWS b/Misc/NEWS
index e873dad..ba98321 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -27,6 +27,10 @@
 
 Core and builtins
 
+- Assignment to __debug__ raises SyntaxError at compile-time.  This
+  was promised when 2.1c1 was released as "What's New in Python 2.1c1"
+  (below) says.
+
 - Clarified the error messages for unsupported operands to an operator
   (like 1 + '').