Make the format of vlog messages user-configurable.

secchan/secchan.8.in

@@ -441,6 +441,11 @@ omitted, \fIlevel\fR defaults to \fBdbg\fR.
 Sets the maximum logging verbosity level, equivalent to
 \fB--verbose=ANY:ANY:dbg\fR.
 
+.TP
+\fB-vPATTERN:\fIfacility\fB:\fIpattern\fR, \fB--verbose=PATTERN:\fIfacility\fB:\fIpattern\fR
+Sets the log pattern for \fIfacility\fR to \fIpattern\fR.  Refer to
+\fBvlogconf\fR(8) for a description of the valid syntax for \fIpattern\fR.
+
 .TP
 .BR \-V ", " \-\^\-version
 Prints version information to the console.