Added Table of Contents to README

[koomai]

This PR adds a Table of Contents section to the README file.

I refer to the README quite often and find the links quite handy. It's very easy to generate. Here's how I do it:

1. Install the markdown-toc npm package globally:

npm i -g markdown-toc

2. Add the below to your README (where you want your Table of Contents to appear):

## Table of Contents
<!-- toc -->
<!-- tocstop -->

3. Run the script in your application's directory:

markdown-toc README.md -i

4. Check the README file and commit your changes.
5. Profit.

Thanks.

[freekmurze]

Thank you for this, but we're not going to merge it. If the readme becomes too big we'll move the docs to our dedicated documentation site.