Fix broken links in Table of Contents (#974)

There were changes in Table of Contents, Getting started to Getting Started with an existing Rails app, Rails Context to Rails Context and Generator Functions and User Content Integration with Node.js for Server Rendering to Integration with Node.js for Server Rendering.

README.md

@@ -138,21 +138,21 @@ React on Rails integrates Facebook's [React](https://github.com/facebook/react)
 
 + [Features](#features)
 + [Why Webpack?](#why-webpack)
-+ [Getting Started](#getting-started)
++ [Getting Started with an existing Rails app](#getting-started-with-an-existing-rails-app)
     - [Installation Overview](#installation-overview)
     - [Initializer Configuration: config/initializers/react_on_rails.rb](#initializer-configuration)
     - [Including your React Component in your Rails Views](#including-your-react-component-in-your-rails-views)
     - [I18n](#i18n)
 + [How it Works](#how-it-works)
     - [Client-Side Rendering vs. Server-Side Rendering](#client-side-rendering-vs-server-side-rendering)
     - [Building the Bundles](#building-the-bundles)
-    - [Rails Context](#rails-context)
+    - [Rails Context and Generator Functions](#rails-context-and-generator-functions)
     - [Globally Exposing Your React Components](#globally-exposing-your-react-components)
     - [ReactOnRails View Helpers API](#reactonrails-view-helpers-api)
     - [ReactOnRails JavaScript API](#reactonrails-javascript-api)
     - [React-Router](#react-router)
     - [Deployment](#deployment)
-+ [Integration with Node.js for Server Rendering](#user-content-integration-with-nodejs-for-server-rendering)
++ [Integration with Node.js for Server Rendering](#integration-with-nodejs-for-server-rendering)
 + [Additional Documentation](#additional-documentation)
 + [Contributing](#contributing)
 + [License](#license)