Pull in socket unit from systemd service (#27)

If the service doesn't pull in the socket unit, the latter will become
unusable until the service exits again.
This way, behavior is consistent no matter if socket activation happened
or the service was started manually/automatically.

yubikey-touch-detector.service

@@ -1,9 +1,11 @@
 [Unit]
 Description=Detects when your YubiKey is waiting for a touch
+Requires=yubikey-touch-detector.socket
 
 [Service]
 ExecStart=/usr/bin/yubikey-touch-detector
 EnvironmentFile=-%E/yubikey-touch-detector/service.conf
 
 [Install]
+Also=yubikey-touch-detector.socket
 WantedBy=default.target