doc/knotc: improve the description of the "zone-purge +orphan" command

doc/man/knotc.8in

@@ -215,11 +215,11 @@ requires a ttl value specified.
 \fBzone\-unset\fP \fIzone\fP \fIowner\fP [\fItype\fP [\fIrdata\fP]]
 Remove zone data within the transaction.
 .TP
-\fBzone\-purge\fP \fIzone\fP\&... [\fIfilter\fP\&...]
+\fBzone\-purge\fP \fIzone\fP\&... [\fB+orphan\fP] [\fIfilter\fP\&...]
 Purge zone data, zone file, journal, timers, and/or KASP data of specified zones.
 Available filters are \fB+expire\fP, \fB+zonefile\fP, \fB+journal\fP, \fB+timers\fP,
 and \fB+kaspdb\fP\&. If no filter is specified, all filters are enabled.
-If the zone is no longer configured, add \fB+orphan\fP filter (zone file cannot
+If the zone is no longer configured, add \fB+orphan\fP parameter (zone file cannot
 be purged in this case). This command always requires the force option. (#)
 .TP
 \fBzone\-stats\fP \fIzone\fP [\fImodule\fP[\fB\&.\fP\fIcounter\fP]]

doc/man_knotc.rst

@@ -192,11 +192,11 @@ Actions
 **zone-unset** *zone* *owner* [*type* [*rdata*]]
   Remove zone data within the transaction.
 
-**zone-purge** *zone*... [*filter*...]
+**zone-purge** *zone*... [**+orphan**] [*filter*...]
   Purge zone data, zone file, journal, timers, and/or KASP data of specified zones.
   Available filters are **+expire**, **+zonefile**, **+journal**, **+timers**,
   and **+kaspdb**. If no filter is specified, all filters are enabled.
-  If the zone is no longer configured, add **+orphan** filter (zone file cannot
+  If the zone is no longer configured, add **+orphan** parameter (zone file cannot
   be purged in this case). This command always requires the force option. (#)
 
 **zone-stats** *zone* [*module*\ [\ **.**\ *counter*\ ]]