Add comment that this schema is invalid

servers/slapd/schema/krb5-kdc.schema

@@ -2,6 +2,10 @@
 # $Id: hdb.schema,v 1.3 2000/02/22 21:51:53 lukeh Exp $
 # Definitions for a Kerberos V KDC schema
 
+#
+# This schema is not usable as it contains invalid constructs.
+#
+
 # OID Base is iso(1) org(3) dod(6) internet(1) private(4) enterprise(1) padl(5322) kdcSchema(10)
 #
 # Syntaxes are under 1.3.6.1.4.1.5322.10.0