Add documentation

[anapaulagomes]

Thanks for creating such nice extension! 🏆 I'd like to list here what I think would be nice to have in a documentation page.

• Introduction: What this extension is about and which problem it solves
• How to install the extension
• Examples
• Troubleshooting

The README already have most of it covered but it's handy to have a documentation where we can search for terms, see the pages available and go directly for what we're looking for.
Here a nice example of documentation: https://dramatiq.io/ (IMHO) They use Sphinx to generate it.

[cuducos]

Closed by #23