Improve docs and set licence headers

This role is licenced under the terms of GPLv3, see GPLv3.txt

vars/main.yml

@@ -1,4 +1,25 @@
 ---
+#  dotqmail/vars/main.yml
+#
+#  Copyright 2016 Jonathan Golder <jonathan@golderweb.de>
+#
+#  This program is free software; you can redistribute it and/or modify
+#  it under the terms of the GNU General Public License as published by
+#  the Free Software Foundation; either version 3 of the License, or
+#  (at your option) any later version.
+#
+#  This program is distributed in the hope that it will be useful,
+#  but WITHOUT ANY WARRANTY; without even the implied warranty of
+#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#  GNU General Public License for more details.
+#
+#  You should have received a copy of the GNU General Public License
+#  along with this program; if not, write to the Free Software
+#  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
+#  MA 02110-1301, USA.
+#
+#
+
 # vars file for dotqmail
 
 # combine dotqmail_default_files from role's default with configuration