Update ArchLinux Download Link

Fixes #896

DOCUMENTATION.md

@@ -1362,8 +1362,8 @@ You can find the source packages of all releases on
 
 Radicale has been packaged for:
 
-  * [ArchLinux (AUR)](https://aur.archlinux.org/packages/radicale/) by
-    Guillaume Bouchard
+  * [ArchLinux](https://www.archlinux.org/packages/community/any/radicale/) by
+    David Runge
   * [Debian](http://packages.debian.org/radicale) by Jonas Smedegaard
   * [Gentoo](https://packages.gentoo.org/packages/www-apps/radicale)
     by René Neumann, Maxim Koltsov and Manuel Rüger