Fixed undocumented config properties for entity_lookup process plugin.

src/Plugin/migrate/process/EntityLookup.php

@@ -14,13 +14,29 @@ use Symfony\Component\DependencyInjection\ContainerInterface;
 /**
  * This plugin looks for existing entities.
  *
- * In its most simple form, this plugin needs no configuration. However, if the
- * lookup properties cannot be determined through introspection, define them via
- * configuration.
+ * In its most simple form, this plugin needs no configuration, and determines
+ * the configuration automatically. This requires the migration's process to
+ * define a default value for the destination entity's bundle key, and the
+ * destination field this plugin is on to be a supported type.
  *
  * Available configuration keys:
+ * - entity_type: (optional) The ID of the entity type to query for.
+ * - value_key: (optional) The name of the entity field on which the source
+ *   value will be queried. If omitted, defaults to one of the following
+ *   depending on the destination field type:
+ *    - entity_reference: The entity label key.
+ *    - file: The uri field.
+ *    - image: The uri field.
+ * - bundle_key: (optional) The name of the bundle field on the entity type
+ *   being queried.
+ * - bundle: (optional) The value to query for the bundle.
  * - access_check: (optional) Indicates if access to the entity for this user
  *   will be checked. Default is true.
+ * - ignore_case: (optional) Whether to ignore case in the query. Defaults to
+ *   true.
+ * - destination_field: (optional) If specified, and if the plugin's source
+ *   value is an array, the result array's items will be themselves arrays of
+ *   the form [destination_field => ENTITY_ID].
  *
  * @codingStandardsIgnoreStart
  *