major release checklist for xarray-selafin

[tomsail]

Putting back in an issue from what I wrote in #58:

These are IMO the following features that would needed for a major version release:

• LazyLoading implented
• Dask support
• robust and exhaustive testing
  • check all BackendEntrypoint subclasses in the tests
  • add a demo notebook in CI
• add online documentation
  • my colleague @pmav99 has experience with mkdocs
  • use the notebook for the docs

I'll create the relevant sub-issues if necessary when time comes