[ci skip] Document `returning` option for bulkCreate

lib/model.js

@@ -2049,6 +2049,7 @@ Model.prototype.insertOrUpdate = Model.prototype.upsert;
  * @param  {Array}        [options.updateOnDuplicate]      Fields to update if row key already exists (on duplicate key update)? (only supported by mysql & mariadb). By default, all fields are updated.
  * @param  {Transaction}  [options.transaction] Transaction to run query under
  * @param  {Function}     [options.logging=false]          A function that gets executed while running the query to log the sql.
+ * @param  {Boolean}      [options.returning=false] Append RETURNING * to get back auto generated values (Postgres only)
  * @param  {String}       [options.searchPath=DEFAULT] An optional parameter to specify the schema search_path (Postgres only)
  *
  * @return {Promise<Array<Instance>>}