Put valid command for onevent in README.

README.md

@@ -42,7 +42,7 @@ backend = alsa
 device = alsa_audio_device # Given by `aplay -L`
 mixer = PCM
 volume-control = alsa # or alsa_linear, or softvol
-onevent = command_run_on_playback_events
+onevent = /usr/bin/echo Playback event! #command_run_on_playback_event
 device_name = name_in_spotify_connect
 bitrate = 96|160|320
 cache_path = cache_directory