mongodb_multi: use perlpod documentation format

plugins/mongodb/mongodb_multi

@@ -1,14 +1,34 @@
-#!/usr/bin/python3 -tt
-# -*- coding: utf-8 -*-
+#!/usr/bin/env python3
 # pylint: disable=invalid-name
 # pylint: enable=invalid-name
 
 """Munin plugin to monitor MongoDB status.
 
-Copyright 2016, Kim B. Heino, b@bbbs.net, Foobar Oy
-License GPLv2+
+=head1 NAME
 
-Based heavily on non-multigraph MongoDB plugin found from github.
+mongodb_multi - monitor MongoDB connections, documents, memory and operations
+
+=head1 APPLICABLE SYSTEMS
+
+Systems with MongoDB installed. Tested up to MongoDB version 4.4.
+
+=head1 CONFIGURATION
+
+Defaults to mongodb://localhost, but can be configured:
+
+    [mongodb_multi]
+    env.uri mongodb://user:password@host:port/dbname?parameters
+
+=head1 AUTHOR
+
+Kim B. Heino <b@bbbs.net>
+
+This is based heavily on non-multigraph MongoDB plugins.
+
+=head1 LICENSE
+
+GPLv2
+=cut
 """
 
 import os