[gimp-web] Add Arch instructions contributed by betseg

[Alexandre Prokoudine <aprokoudine src gnome org>]

commit 821c70d77fe400fab9f954a6ea96bbc471f01170
Author: Alexandre Prokoudine <alexandre prokoudine gmail com>
Date:   Sun Nov 22 15:15:06 2015 +0300

    Add Arch instructions contributed by betseg

 content/downloads/index.md |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/content/downloads/index.md b/content/downloads/index.md
index 1156f93..bda7616 100644
--- a/content/downloads/index.md
+++ b/content/downloads/index.md
@@ -124,6 +124,10 @@ Similarly to the above, Fedora users can install GIMP by running `dnf install gi
 
 Gentoo users can install GIMP by running `emerge gimp` for the latest stable version.
 
+### Arch
+
+Arch Linux users can install GIMP by running `pacman -S gimp`.
+
 ### Mageia 
 
 Mageia Linux users can install GIMP by running `urpmi gimp`.