Issue #3263877: DefaultEntityValue - document configuration properties and improve documentation

Closes #3263877

src/Plugin/migrate/process/DefaultEntityValue.php

@@ -9,7 +9,7 @@ use Drupal\migrate\Row;
  * Returns EntityLookup for a given default value if input is empty.
  *
  * Available configuration keys:
- * - default_value: The default value that will be used as for entity lookup.
+ * - default_value: The default value that will be used as for the entity lookup.
  * For additional configuration keys, refer to the parent class.
  *
  * Example:
@@ -28,8 +28,9 @@ use Drupal\migrate\Row;
  *       default_value: editorial
  * @endcode
  *
- * In this example the user with "editorial" name will be assigned to 'uid'
- * destination property if the original author was not found during lookup.
+ * In this example, it will look up the source value of author in the users
+ * migration and if not found, use entity lookup to find a user with "editorial"
+ * username.
  *
  * @see \Drupal\migrate_plus\Plugin\migrate\process\EntityLookup
  *