Add a link to the unofficial AUR package

Author: Ortham

index.html

@@ -11,4 +11,6 @@
     <button class="mdl-button mdl-js-button mdl-button--raised mdl-button--accent mdl-js-ripple-effect">Download LOOT</button>
 </a></p>
 
+<p>An unofficial <a href="https://aur.archlinux.org/packages/loot">AUR package</a> is also available for users of Arch-based Linux distributions.</p>
+
 <p>While we welcome user feedback, please check the <a href="/docs/help/LOOT-FAQs.html">FAQs</a> in case you have a question that has already been answered. If you wish to report an issue, please read the <a href="/docs/help/How-To-Report-Issues-Helpfully.html">How To Report Issues Helpfully</a> page for instructions.</p>