Add documentation for event example properties

[romm]

See:

NotiZ/Classes/Core/Event/Support/ProvidesExampleProperties.php

Lines 19 to 49 in af8cb88

	/**
	* Interface that can be implemented by an event to give example properties that
	* will be used in the backend module to show a preview of a notification bound
	* to this event.
	*
	* Example:
	*
	* ```
	* class MyEvent implements Event, ProvidesExampleProperties
	* {
	* protected $someValue;
	*
	* public function getExampleProperties()
	* {
	* return [
	* 'someValue' => 'Some value example',
	* ];
	* }
	* }
	* ```
	*/
	interface ProvidesExampleProperties
	{
	/**
	* Returns an array in which the key of an entry is the name of a property
	* and its value is a human-readable example value.
	*
	* @return array
	*/
	public function getExampleProperties();
	}