docs: Start automatically with Systemd

I found the systemd user service works wonderfully, with the only exception that even after adding the required pre-requsite units, `noisetorch -i ...` returns exit code `0` without actually loading the filters. I found that adding a small sleep improves the reliability of the unit file and allows everything to start running smoothly. I propose the unit file in the Wiki gets amended with the addition of `ExecStartPre=/bin/sleep 5`, to: ```py [Unit] Description=Noisetorch Noise Cancelling Requires=$DEVICEUNIT After=$DEVICEUNIT # Depending on if you're using pulseaudio or pipewire, uncomment the correct line # After=pulseaudio.service # After=pipewire.service [Service] Type=simple RemainAfterExit=yes ExecStartPre=/bin/sleep 5 ExecStart=%h/.local/bin/noisetorch -i -s $DEVICEID -t 95 ExecStop=%h/.local/bin/noisetorch -u Restart=on-failure RestartSec=3 [Install] WantedBy=default.target ```