Support command-not-found on Arch Linux

Signed-off-by: Sorin Ionescu <sorin.ionescu@gmail.com>

modules/command-not-found/README.md

@@ -1,7 +1,8 @@
 Command-Not-Found
 =================
 
-Loads the [command-not-found][1] tool on Debian-based distributions.
+Displays installation information for not found commands by loading the
+[command-not-found][1] tool on Debian-based and Arch Linux-based distributions.
 
 Authors
 -------

modules/command-not-found/init.zsh

@@ -5,10 +5,14 @@
 #   Joseph Jon Booker <joe@neoturbine.net>
 #
 
+# Load command-not-found on Debian-based distributions.
+if [[ -s '/etc/zsh_command_not_found' ]]; then
+  source '/etc/zsh_command_not_found'
+# Load command-not-found on Arch Linux-based distributions.
+elif [[ -s '/usr/share/doc/pkgfile/command-not-found.zsh' ]]; then
+  source '/usr/share/doc/pkgfile/command-not-found.zsh'
 # Return if requirements are not found.
-if [[ ! -s '/etc/zsh_command_not_found' ]]; then
+else
   return 1
 fi
 
-source '/etc/zsh_command_not_found'
-