license added (MIT)

README.md

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 # ISPmail Jessie Ansible Playbook #
 
 This repository contains a playbook and roles that you can use to set up your own Debian-based mail server. Please follow the instructions at https://workaround.org/ispmail/jessie/ansible
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+# License #
+
+Everything in this repository can be freely used under the terms of the MIT license.