Add hello-world exercise

[ErikSchierboom]

Each track must have a practice exercise named hello-world, which should have students just return the text "Hello, World!"

Tracking

exercism/v3-launch#34

[Newby555]

This has been addressed. Is there anything else that needs to be done to launch the track?

[ErikSchierboom]

Great! Looking at the data in this repository, I found the following open issues:

• The snippet needs to be populated
• The CI and PR workflows should check whether the exercises are correct. The usual way to have these workflows go over each exercise and check if the example implementation passes all the tests.
• While not strictly necessary, it would be nice if this track had a test runner. This would enable students to use our bew in-browser editor. See https://github.com/exercism/docs/blob/main/building/tooling/test-runners/README.md for more docs. We have a generic-test-runner to build on to help you get started.
• We usually require tracks to launch with 20-ish exercises. But seeing that this track is quite different, it might be okay to launch with less. I'll discuss with @iHiD