Start to document components

[fengelniederhammer]

resolves #129

Summary

This is mostly meant to update the README as a preparation to publish a first version as an NPM package.

This also sketches how we can document components using Storybook. If you like this approach, we can create follow-up issues to document all existing components.

Screenshot

This is the Storybook docs page for the location filter. Most parts of this are autogenerated from the custom-elements.json.

PR Checklist

• [ ] The implemented feature is covered by an appropriate test.

[fengelniederhammer]

If we notice that there is a pattern across all components, we can also think about using a customized docs template: https://storybook.js.org/docs/writing-docs/doc-blocks#customizing-the-automatic-docs-page

[JonasKellerer]

Great start.
LGTM.