iptables: manpage updates for augmented -Z syntax

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
diff --git a/iptables.8.in b/iptables.8.in
index 6125e65..928f46a 100644
--- a/iptables.8.in
+++ b/iptables.8.in
@@ -35,7 +35,7 @@
 .PP
 \fBiptables\fP [\fB\-t\fP \fItable\fP] \fB\-S\fP [\fIchain\fP [\fIrulenum\fP]]
 .PP
-\fBiptables\fP [\fB\-t\fP \fItable\fP] {\fB\-F\fP|\fB\-L\fP|\fB\-Z\fP} [\fIchain\fP] [\fIoptions...\fP]
+\fBiptables\fP [\fB\-t\fP \fItable\fP] {\fB\-F\fP|\fB\-L\fP|\fB\-Z\fP} [\fIchain\fP [\fIrulenum\fP]] [\fIoptions...\fP]
 .PP
 \fBiptables\fP [\fB\-t\fP \fItable\fP] \fB\-N\fP \fIchain\fP
 .PP
@@ -189,8 +189,9 @@
 Flush the selected chain (all the chains in the table if none is given).
 This is equivalent to deleting all the rules one by one.
 .TP
-\fB\-Z\fP, \fB\-\-zero\fP [\fIchain\fP]
-Zero the packet and byte counters in all chains.  It is legal to
+\fB\-Z\fP, \fB\-\-zero\fP [\fIchain\fP [\fIrulenum\fP]]
+Zero the packet and byte counters in all chains, or only the given chain,
+or only the given rule in a chain. It is legal to
 specify the
 \fB\-L\fP, \fB\-\-list\fP
 (list) option as well, to see the counters immediately before they are