Add Xandikos server.

README.md

@@ -223,6 +223,7 @@ _CalDAV or CardDAV servers_
 - [EteSync Server](https://www.etesync.com) - End-to-end encrypted and journaled personal information server supporting calendar and contact data, offering its own clients. ([Source Code](https://github.com/etesync/server-skeleton)) `AGPL-3.0` `Python/Django`
 - [Radicale](http://radicale.org/) - Simple calendar and contact server with extremely low administrative overhead. ([Source Code](https://github.com/Kozea/Radicale)) `GPL-3.0` `Python`
 - [SabreDAV](http://sabre.io/) - Open source CardDAV, CalDAV, and WebDAV framework and server. ([Source Code](https://github.com/sabre-io/dav)) `MIT` `PHP`
+- [Xandikos](https://www.xandikos.org/) - Open source CardDAV, CalDAV and WebDAV server with minimal administrative overhead, backed by a Git repository. ([Source Code](https://github.com/jelmer/xandikos)) `GPL-3.0` `Python`
 
 _CalDAV or CardDAV clients._