[zpool_iostat] add POD documentation

plugins/zfs/zpool_iostat

@@ -3,6 +3,42 @@
 
 set -eu
 
+: <<=cut
+
+=head1 NAME
+
+zpool_iostat - Plugin to monitor transfer statistics of ZFS pools
+
+=head1 APPLICABLE SYSTEMS
+
+All systems with "zpool" installed.
+
+=head1 CONFIGURATION
+
+No configuration is required.
+
+=head1 INTERPRETATION
+
+This plugin shows a graph with read (positive) and write (negative) values
+for the IO transfer of each pool.
+
+=head1 MAGIC MARKERS
+
+  #%# family=auto
+  #%# capabilities=autoconf
+
+=head1 AUTHOR
+
+tsaavik <github@hellspark.com>
+Peter Doherty <peterd@acranox.org>
+Lars Kruse <devel@sumpfralle.de>
+
+=head1 LICENSE
+
+GPLv2
+
+=cut
+
 
 # shellcheck source=/usr/share/munin/plugins/plugin.sh
 . "$MUNIN_LIBDIR/plugins/plugin.sh"