Add local_auth to README.md (flutter#201)

Author: mit-mit

README.md

@@ -24,6 +24,7 @@ These are the available plugins in this repository.
 | [device info](./packages/device_info/) | [![pub package](https://img.shields.io/pub/v/device_info.svg)](https://pub.dartlang.org/packages/device_info) |
 | [google_sign_in](./packages/google_sign_in/) | [![pub package](https://img.shields.io/pub/v/google_sign_in.svg)](https://pub.dartlang.org/packages/google_sign_in) |
 | [image_picker](./packages/image_picker/) | [![pub package](https://img.shields.io/pub/v/image_picker.svg)](https://pub.dartlang.org/packages/image_picker) |
+| [local_auth](./packages/local_auth/) | [![pub package](https://img.shields.io/pub/v/local_auth.svg)](https://pub.dartlang.org/packages/local_auth) |
 | [package_info](./packages/package_info/) | [![pub package](https://img.shields.io/pub/v/package_info.svg)](https://pub.dartlang.org/packages/package_info) |
 | [path_provider](./packages/path_provider/) | [![pub package](https://img.shields.io/pub/v/path_provider.svg)](https://pub.dartlang.org/packages/path_provider) |
 | [quick_actions](./packages/quick_actions/) | [![pub package](https://img.shields.io/pub/v/quick_actions.svg)](https://pub.dartlang.org/packages/quick_actions) |