Fix syntax error

Fixes an error that happens when trying to run the example:
$ nc -w 1 localhost 4532P
nc: port number invalid: 4532P

doc/man1/rigctld.1

@@ -1741,7 +1741,7 @@ default protocol from the shell prompt:
 .PP
 .in +4n
 .EX
-$ \fBecho "\\set_freq 14266000" | nc -w 1 localhost 4532\P
+$ \fBecho "\\set_freq 14266000" | nc -w 1 localhost 4532\fP
 .EE
 .in
 .