Improve crs tutorial

[amsnyder]

This tutorial could use a bit of work:

• It would be great if the Adding CRS to a Regular Zarr Store actually performed the function on a zarr store.
• I would like a discussion of what to look for to ensure your crs variable is cf-compliant (or at least how you can use a python package to check it)
• I would like a discussion of how to add a crs variable if it is missing
• I think we should also show how to update a crs variable if it is incorrect