diff --git a/beets/__main__.py b/beets/__main__.py
index 7b5fc798f..5f10c5b9b 100644
--- a/beets/__main__.py
+++ b/beets/__main__.py
@@ -1,5 +1,31 @@
-"""main module."""
 # -*- coding: utf-8 -*-
+"""main module.
+
+This module will be executed when beets module is run with `-m`.
+
+Example : `python -m beets`
+
+Related links about __main__.py:
+
+* python3 docs entry: https://docs.python.org/3/library/__main__.html
+* related SO: http://stackoverflow.com/q/4042905
+"""
+# This file is part of beets.
+# Copyright 2017, Adrian Sampson.
+#
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+#
+# The above copyright notice and this permission notice shall be
+# included in all copies or substantial portions of the Software.
+
+from __future__ import division, absolute_import, print_function
+
 import sys
 from .ui import main