Update downloading.md

Add the AUR package.

Author: mchalupa

doc/downloading.md

@@ -2,7 +2,11 @@
 
 You can obtain pre-compiled DG project in several forms.
 
-## Docker images
+## Docker image
 
 You can download the image from [Docker Hub](https://hub.docker.com/r/mchalupa/dg). The image
 contains, apart from DG, also vim and emacs editors and clang, so you can try dg out!
+
+## Archlinux AUR package
+
+There is also the [dg-git](https://aur.archlinux.org/packages/dg-git/) AUR package for Archlinux users.