[Feature] Specify units for voxel sizes in napari plugin

[dstansby]

Is your feature request related to a problem? Please describe.
I was reading https://brainglobe.info/tutorials/tutorial-whole-brain-registration.html and thinking about trying to register a brain from the Human Organ Atlas. One of the first parameters that needs setting is the voxel size. It's not clear from the screenshots of the napari plugin what units these are in however.

Describe the solution you'd like
An indication in the GUI of what units the voxel size is in.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.

[adamltyson]

Definitely an oversight on our part. We'll add it to the docs, but do you think it should be added to the main GUI (e.g. voxel size (z), um), or would adding it to the tooltip be sufficient?

BTW I wouldn't expect brainreg to work well for your data, we don't really have a suitable human brain atlas (yet).

[dstansby]

I'd be pretty pro having it explicitly in the GUI. Thanks for heads up on the human atlas!

[adamltyson]

We'd like to gradually support more human atlases, but not sure which one would be best for your application. TemplateFlow may be useful for you.