* Search for Spotify directory if not found in PATH
* Update install.sh
* Confirm directory provided with `-P` exists
* Confirm xpui exists in `-P` directory
- add `-P` flag to manually set Spotify path
- add support for enabling write permissions in Spotify directory if write permissions are not found (thanks to @dabiathenord for the heads up)
- update readme for path flag and to note that Snap installs are not supported
