Added Mailu demo link, fixed platform

README.md

@@ -264,7 +264,7 @@ _simple deployment of a mail server, e.g. for inexperienced or impatient admins.
   * [docker-mailserver](https://github.com/tomav/docker-mailserver) - A fullstack but simple mail server (smtp, imap, antispam, antivirus, etc.). Only configuration files, no SQL database. Keep it simple and versioned. Easy to deploy and upgrade. `MIT` `Docker`
   * [iRedMail](http://www.iredmail.org/) - Full-featured mail server solution based on Postfix and Dovecot. ([Source Code](https://bitbucket.org/zhb/iredmail/commits/)) `GPLv3` `Shell`
   * [Mailcow](https://mailcow.email/) - Mail server suite based on Dovecot, Postfix and other open source software, that provides a modern Web UI for administration. ([Source Code](https://github.com/andryyy/mailcow)) `GPLv2` `PHP`
-  * [Mailu](https://mailu.io/) - Mailu is a simple yet full-featured mail server as a set of Docker images. ([Source Code](https://github.com/Mailu/Mailu)) `MIT` `PHP`
+  * [Mailu](https://mailu.io/) - Mailu is a simple yet full-featured mail server as a set of Docker images. ([Demo](https://github.com/Mailu/Mailu/wiki/Demo-server), [Source Code](https://github.com/Mailu/Mailu)) `MIT` `Docker/Python`
   * [Mail-in-a-Box](https://mailinabox.email/) - Turns any Ubuntu server into a fully functional mail server with one command. ([Source Code](https://github.com/mail-in-a-box/mailinabox)) `CC0` `Shell`
   * [Modoboa](http://modoboa.org/en/) - Modoboa is a mail hosting and management platform including a modern and simplified Web User Interface. ([Source Code](https://github.com/tonioo/modoboa)) `MIT` `Python`