Add missing parameter to the JSDoc of findOrCreate

lib/model.js

@@ -1599,6 +1599,7 @@ Model.prototype.findOrInitialize = Model.prototype.findOrBuild = function(option
  * @param {Object}      options
  * @param {Object}      options.where where A hash of search attributes.
  * @param {Object}      [options.defaults] Default values to use if creating a new instance
+ * @param {Transaction} [options.transaction] Transaction to run query under. See above for detail
  * @see {Model#findAll} for a specification of find and options
  * @return {Promise<Instance,created>}
  */