Hello World sample App

This PR intends to add an extremely simple of the demo apps repo, this App is used for training purposes and is the perfect app to use if you have 20 mns and want to explain to someone how the framework works

The goal is to get to this

We'll start without some of these elements and ask "students" to work their way through it

cc @zendesk/quokka 

Tasks:

- [x] Basic App structure
- [ ] Readme
- [ ] Licence file