Document reserved words for PQ+

Change-Id: Icb3c360481a93206d6ebbf5823f9f3bde7d8855d
diff --git a/Changes b/Changes
index cf6c712..262f721 100755
--- a/Changes
+++ b/Changes
@@ -1,8 +1,9 @@
-0.51 2023-06-09
+0.51 2023-07-21
         - Support defined log file in configuration. (diewald)
         - Remove experimental_client_registration setting
           and make client registration mandatory in OAuth
           (diewald)
+        - Introduce 'reserved terms' in documentation (diewald)
 
 0.50 2023-05-08
         - Improvement of NKJP-annotation helper. (diewald)