added spam result detection support

etc/example.conf

@@ -48,6 +48,22 @@ piler_header_field=X-piler: piler already archived this email
 ; the direction of the given email
 mydomains=
 
+
+; if piler detects this line in the mail header, then it will assume
+; the message is a spam. You should include your own antispam solution's
+; specific line.
+;
+; If you use SpamAssassin you may use
+;
+; spam_header_line=X-Spam-Status: Yes
+;
+; OR
+;
+; spam_header_line=X-Spam-Level: ********
+;
+; The default value is empty.
+spam_header_line=
+
 ;
 ; memcached stuff
 ;