[flutter_appauth] updated readme to add a table of contents (#595)

* added table of contents to readme

* updated table of contents and location

* added changelog entry for toc addition

flutter_appauth/CHANGELOG.md

@@ -7,6 +7,7 @@
 * Migrated Android side of example to use plugin DSL
 * Bumped `flutter_lints` dev dependency
 * Fixed typo in the code snippet shown in the **End session** section of the readme. Thanks to the PR from [barryguvenkaya](https://github.com/barryguvenkaya)
+* Updated readme to add a table of contents
 
 ## [8.0.2]
 

flutter_appauth/README.md

@@ -3,6 +3,21 @@
 [![pub package](https://img.shields.io/pub/v/flutter_appauth.svg)](https://pub.dartlang.org/packages/flutter_appauth)
 [![Build Status](https://api.cirrus-ci.com/github/MaikuB/flutter_appauth.svg)](https://cirrus-ci.com/github/MaikuB/flutter_appauth/)
 
+- [Introduction](#introduction)
+- [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)
+
+
+## Introduction 
 A Flutter bridge for AppAuth (https://appauth.io) used authenticating and authorizing users. Note that AppAuth also supports the PKCE extension that is required some providers so this plugin should work with them.
 
 **IMPORTANT NOTES**: