Update documentation for Entity::has().

Reflect how the code actually works.

Refs #8494

src/Datasource/EntityTrait.php

@@ -317,7 +317,7 @@ public function getOriginal($property)
 
     /**
      * Returns whether this entity contains a property named $property
-     * regardless of if it is empty.
+     * that contains a non-null value.
      *
      * ### Example:
      *
@@ -328,6 +328,14 @@ public function getOriginal($property)
      * $entity->has('last_name'); // false
      * ```
      *
+     * You can check multiple properties by passing an array:
+     *
+     * ```
+     * $entity->has(['name', 'last_name']);
+     * ```
+     *
+     * All properties must not be null to get a truthy result.
+     *
      * When checking multiple properties. All properties must not be null
      * in order for true to be returned.
      *