Merge pull request #172 from Envek/patch-1

Add link to imgproxy package in AUR for Arch Linux users

docs/installation.md

@@ -1,6 +1,6 @@
 # Installation
 
-There are three ways you can install imgproxy:
+There are four ways you can install imgproxy:
 
 ### Docker
 
@@ -33,6 +33,12 @@ $ heroku stack:set container
 $ git push heroku master
 ```
 
+### Packages
+
+#### Arch Linux and derivatives
+
+[imgproxy](https://aur.archlinux.org/packages/imgproxy/) package is available from AUR.
+
 ### From the source
 
 #### Ubuntu