Document (or fix) explicitly that :WILD_NOTIFIER_NOTIFY_BEFORE: keyword requires SCHEDULED: stamp

[dalanicolai]

While this package does not require a SCHEDULED: stamp for "default" notifications, using the :WILD_NOTIFIER_NOTIFY_BEFORE: does require an additional SCHEDULED: stamp to work. This is not EXPLICITLY documented (other than just showing it in the example), and it can be rather confusing.

Would be great if you could add it to the README or alternatively, make it work without the SCHEDULED: stamp.

Otherwise, thanks for the very nice package!