Add detection for spotify-launcher install location on Arch

[LegitGreenBoi]

On Arch you can either install Spotify using the AUR 'spotify' package or the community repository 'spotify-launcher' package. SpotX successfully detects the AUR package Spotify install, but not the spotify-launcher package install. Using the path argument works as a workaround, but it would be nice for the directory to be automatically detected.

spotify-launcher installs Spotify to this directory: ~/.local/share/spotify-launcher/install/usr/share/spotify

EDIT: For anyone still wondering, SpotX's official Bash version supports spotify-launcher and it looks like this repository is no longer needed or supported. Here's the official version, use this instead: https://github.com/SpotX-Official/SpotX-Bash