Add quickstart example

[kostasx]

As an educator I've heard a lot of students complaining about the lack of a simpler setup example on the documentation.
Something like a 'Hello World' for RTL to get them started before diving into the extensive full example.

I think this quickstart example will help newcomers start with a simple setup, test it out on their project and move on from there to the more advanced concepts and probably to the Full example in this page.

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[eps1lon]

Much appreciated, thanks! Just one minor adjustment needed

[ph-fritsche]

Let's point beginners towards the recommended interaction testing instead of the escape hatch.

[eps1lon]

@all-contributors add @kostasx for docs

[allcontributors]

@eps1lon

I've put up a pull request to add @kostasx! 🎉