add (fork of Airtime) to Libretime entry

README.md

@@ -773,7 +773,7 @@ See also <https://en.wikipedia.org/wiki/List_of_streaming_media_systems>, <https
   * [Icecast 2](http://www.icecast.org/) - streaming audio/video server which can be used to create an Internet radio station or a privately running jukebox and many things in between. ([Source Code](https://git.xiph.org/?p=icecast-server.git;a=summary)) `GPLv2` `C`
   * [koel](http://koel.phanan.net/) - A personal music streaming server that works. ([Source Code](https://github.com/phanan/koel)) `MIT` `PHP`
   * [Libresonic](http://libresonic.org/) - Open-source web-based media streamer and jukebox. A fork of Subsonic's last open-source release, before it switched licenses. `GPLv3` `Java`
-  * [LibreTime](http://libretime.org) - Simple, open source platform that lets you broadcast streaming radio on the web. ([Source Code](https://github.com/LibreTime/libretime)) `AGPLv3` `PHP`
+  * [LibreTime](http://libretime.org) - Simple, open source platform that lets you broadcast streaming radio on the web (fork of [Airtime](https://github.com/sourcefabric/Airtime)). ([Source Code](https://github.com/LibreTime/libretime)) `AGPLv3` `PHP`
   * [Mopidy](http://mopidy.readthedocs.org/) - Extensible music server. Offers a superset of the mpd API, as well as integration with 3rd party services like Spotify, SoundCloud etc. ([Source Code](https://github.com/mopidy/mopidy)) `Apache` `Python`
     * [Moped](https://github.com/martijnboland/moped) - Responsive HTML5 + Javascript client for the Mopidy music server. `MIT` `HTML5`
     * [Mopidy MusicBox](https://github.com/pimusicbox/mopidy-musicbox-webclient) - Web Client for Mopidy Music Server. `Apache` `HTML5`