Add documentation to run and test image locally

[batpad]

I'm imagining it should be relatively easy to run the image locally and get the Jupyterlab interface at some port, to be able to test the image locally - and most importantly, for the person writing the notebook tests to be able to test those test notebooks locally.

@sunu would you be able to add / link to docs on the best way to do that? Thanks!

[sunu]

We already have some documentation on that: https://github.com/NASA-IMPACT/pangeo-notebook-veda-image?tab=readme-ov-file#testing-the-image

I'll update those docs to add some more details and a script to run the tests locally.

[batpad]

Sorry @sunu I some-how just missed that - don't think I'd finished my morning coffee yet.