VirtualiZarr example

[tomwhite]

This is the example I was working on at the Post-AGU Pangeo Hack Day on Saturday.

The idea is to take multiple NetCDF files, combine with VirtualiZarr, and then rechunk using Cubed. This works, although there are some rough edges still. Also, when I tried using Icechunk rather than Kerchunk to write the references, I got an error when reading them back, so that needs investigating too.