Fix Arch Linux .install file

simple_backup.install

@@ -1,5 +1,5 @@
 post_install() {
-   echo "An example configuration file is found in /etc/simple_backup/config."
+   echo "An example configuration file is found in /etc/simple_backup/simple_backup.config."
    echo "Copy it to ~/.simple_backup/simple_backup.config and modify it as needed"
 }