Docs: wrong muti file picker usage

README.md

@@ -90,6 +90,7 @@ if (result != null) {
 #### Multiple files with extension filter
 ```dart
 FilePickerResult? result = await FilePicker.platform.pickFiles(
+  allowMultiple: true,
   type: FileType.custom,
   allowedExtensions: ['jpg', 'pdf', 'doc'],
 );