Add comment about patch.

mail/spamass-milter/Makefile

@@ -1,14 +1,19 @@
-# $NetBSD: Makefile,v 1.29 2010/06/05 13:45:12 gdt Exp $
+# $NetBSD: Makefile,v 1.30 2010/06/10 12:30:21 gdt Exp $
 #
 
 DISTNAME=	spamass-milter-0.3.1
 PKGREVISION=	3
 CATEGORIES=	mail
 MASTER_SITES=	http://savannah.nongnu.org/download/spamass-milt/
 
+# This patch is taken from upstream CVS, and is from the 0.3.1 release
+# tag to head of CVS on 5 Jun 2010, although CVS last changed on 24
+# Jul 2006.  The patch fixes an error in formatting of the synthetic
+# Received: line.  The patch is a patchfile (hosted on ftp.netbsd.org)
+# instead of a pkgsrc patch because it is something upstream would
+# have released if upstream were still maintaining this code.
 PATCHFILES=	spamass-milter-001.patch
 
-
 MAINTAINER=	gdt@NetBSD.org
 HOMEPAGE=	http://savannah.nongnu.org/projects/spamass-milt/
 COMMENT=	Milter interface to Spamassassin