Executable code examples in docs

[TomNicholas]

The main usage docs revolve around code examples, but these are currently just hard-coded in. It would be good to generate these results automatically, and even better if the docs would display the lovely xarray HTML repr instead of the boring string repr.

I'm not sure what the best way to set that up with myst-markdown is. Do I need to rewrite the usage.md page as a jupyter notebook?

[ayushnag]

Yes, if you use jupyter notebook files they will show the xarray HTML output. They can also be auto executed on compilation: https://jupyterbook.org/en/stable/content/execute.html

[maxrjones]

If we use mkdocs (#500), we can use https://pawamoy.github.io/markdown-exec/ to execute code blocks in markdown.

[maxrjones]

The usage guide includes executed codeblocks after #701