Update readme. Async request parameter.

Author: AleksandrRogov

README.md

@@ -178,6 +178,7 @@ an invalid property you will receive either an error saying that the request is
 
 Property Name | Type | Operation(s) Supported | Description
 ------------ | ------------- | ------------- | -------------
+async | Boolean | All | **Important! XHR requests only!** Indicates whether the requests should be made synchronously or asynchronously. Default value is `true` (asynchronously).
 collection | String | All | The name of the Entity Collection, for example, for `account` use `accounts`, `opportunity` - `opportunities` and etc.
 count | Boolean | `retrieveMultipleRequest`, `retrieveAllRequest` | Boolean that sets the $count system query option with a value of true to include a count of entities that match the filter criteria up to 5000 (per page). Do not use $top with $count!
 entity | Object | `updateRequest`, `upsertRequest` | A JavaScript object with properties corresponding to the logical name of entity attributes (exceptions are lookups and single-valued navigation properties).