Zarr for Points

[wildintellect]

We need to make sure to mention not all Zarr data needs to be regularly gridded.
In fact you can use Zarr for Point data - and data retrieval can be fast. We should get an example we can share from @bitner

Then there's the whole irregular grid stuff, should probably skip that for now.

[abarciauskas-bgse]

@bitner if you have an example I will try and incorporate it