Tags in md files require square brackets for jupytext

[tobydriscoll]

When I use tags as shown in the docs, jupytext gives an error:

nbformat.validator.NotebookValidationError: 'remove-input' is not of type 'array'

Failed validating 'type' in notebook['properties']['metadata']['properties']['tags']:

On instance['metadata']['tags']:
'remove-input'

When the tag is put inside array brackets, the conversion is successful.

(jupytext v1.16.4)

[rowanc1]

Do you agree that this is a documentation improvement in mystmd? That is, we default to documenting only the array, and/or is this a validation issue that we can request from jupytext to allow that tool to be more permissive with their coercion and validation around tags.

Happy to take a PR with improving the mystmd docs and moving the examples towards recommending arrays.