[Minor] Update HFILTER_HOSTNAME_UNKNOWN description

conf/scores.d/hfilter_group.conf

@@ -114,7 +114,7 @@ symbols = {
 */
     "HFILTER_HOSTNAME_UNKNOWN" {
         weight = 2.50;
-        description = "Unknown hostname (no PTR or no resolve PTR to hostname)";
+        description = "Unknown client hostname (PTR or FCrDNS verification failed)";
     }
     "HFILTER_RCPT_BOUNCEMOREONE" {
         weight = 1.50;
@@ -128,4 +128,4 @@ symbols = {
         weight = 2.50;
         description = "One line URL and text in body";
     }
-}
+}