Current attribution text is too verbose, and does not work for small maps, e.g. here

Mapbox has a good style of attribution that I think we should follow - it provides a link to https://www.openstreetmap.org/about/ - very concise and easy to read "about" page.

I propose a simple "© OpenStreetMap" linking to the about page in the bottom right corner.

Once we have a good "improve map" link, we should add it as well.