Add a map

[Simon Willison]

The site deserves a map.

There's a secret one at https://www.niche-museums.com/browse/museums but I want an appropriately styled one at /map that's linked from the navigation.

Depends on simonw/datasette#648

[Simon Willison]

Implemented in 1168b95 and b262a92 - I decided not to block this on waiting for the Datasette feature.