added table of contents to readme

flutter_appauth/README.md

@@ -1,3 +1,17 @@
+- [Flutter AppAuth Plugin](#flutter-appauth-plugin)
+  - [Tutorials from identity providers](#tutorials-from-identity-providers)
+  - [Getting Started](#getting-started)
+    - [Detecting user cancellation](#detecting-user-cancellation)
+    - [Refreshing tokens](#refreshing-tokens)
+    - [End session](#end-session)
+    - [Handling errors](#handling-errors)
+    - [Ephemeral Sessions (iOS and macOS only)](#ephemeral-sessions-ios-and-macos-only)
+  - [Android setup](#android-setup)
+  - [iOS/macOS setup](#iosmacos-setup)
+  - [API docs](#api-docs)
+  - [FAQs](#faqs)
+
+
 # Flutter AppAuth Plugin
 
 [![pub package](https://img.shields.io/pub/v/flutter_appauth.svg)](https://pub.dartlang.org/packages/flutter_appauth)