Rename the folder `documentation` to `docs` and enable Github Pages

We should consider using GitHub Pages to build a site for our documentation for this project.

- [ ] Rename the folder `documentation` to `docs`
- [ ] Add setup like what we [have on filmfolk repo](https://github.com/itk-dev/filmfolk/tree/develop/docs)
- [ ] [Enable Pages](https://github.com/itk-dev/deltag.aarhus.dk/settings/pages) on branch `main`