Plugin cpu_freq_1sec: convert documentation to perldoc format

plugins/raspberry-pi/cpu_freq_1sec

@@ -1,9 +1,25 @@
 #! /bin/sh
-#
-# This is a small supersampling plugin that does
-# cpu sampling every 1 second.
-#
-# (c) 2013 - LGPL - Steve Schnepp <steve.schnepp@pwkf.org>
+
+: <<=cut
+
+=head1 NAME
+
+cpu_freq_1sec - small supersampling plugin that samples cpu usage every second
+
+
+=head1 AUTHORS
+
+Copyright (C) 2013 Steve Schnepp <steve.schnepp@pwkf.org>
+
+
+=head1 LICENSE
+
+GNU Library General Public License v2 only
+
+SPDX-License-Identifier: LGPL-2.0-only
+
+=cut
+
 
 pluginfull="$0"                 # full name of plugin
 plugin="${0##*/}"               # name of plugin