Install systemd user service (and load config from XDG dir)

[haasn]

For now, I'm using this:

[Unit]
Description=Shairport Sync - AirPlay Audio Receiver
After=sound.target
Wants=network-online.target
After=network.target network-online.target

[Service]
ProtectSystem=full
ProtectHome=read-only
ExecStart=/usr/bin/shairport-sync --configfile=%h/.config/shairport-sync.conf --verbose --log-to-syslog

[Install]
WantedBy=default.target

But it would be better to have the install script automatically install a unit file (with corrected paths), as well as pulling the config from $XDG_CONFIG_DIR in addition to /etc