Document the optional params

docs/api/app.md

@@ -448,11 +448,13 @@ bar, and on macOS you can visit it from dock menu.
 
 Clears the recent documents list.
 
-### `app.setAsDefaultProtocolClient(protocol)` _macOS_ _Windows_
+### `app.setAsDefaultProtocolClient(protocol[, path, args])` _macOS_ _Windows_
 
 * `protocol` String - The name of your protocol, without `://`. If you want your
   app to handle `electron://` links, call this method with `electron` as the
   parameter.
+* `path` String (optional) _Windows_
+* `args` Array (options) _Windows_
 
 This method sets the current executable as the default handler for a protocol
 (aka URI scheme). It allows you to integrate your app deeper into the operating
@@ -460,6 +462,9 @@ system. Once registered, all links with `your-protocol://` will be opened with
 the current executable. The whole link, including protocol, will be passed to
 your application as a parameter.
 
+On windows you can provide optional parameters path, the path to your executable,
+and args, an array of arguments to be passed to your executable when it launches.
+
 Returns `true` when the call succeeded, otherwise returns `false`.
 
 **Note:** On macOS, you can only register protocols that have been added to