If you just want it to auto-start at login, you could create a symlink from the .desktop file to ~/.config/autostart
.
Something like ln ~/.local/applications/spotify.desktop ~/.config/autostart
(or ln /usr/share/applications/spotify.desktop ~/.config/autostart
if that’s where it installed to).
I believe most DE’s will pick this up automatically.
Ahh I thought they were just making a service for the normal spotify application, yeah in that case it makes sense to use a service. Didn’t know spotifyd is something else