add notebook demonstrating the difference between `cle.scale` and `skimage.transform.downscale_local_mean`

[thawn]

cle.skale essentially preserves noise when downscaling. skimage.transform.downscale_local_mean, on the other hand, denoises at the same time.

I would like to add a notebook that demonstrates this.

[thawn]

Just give me a few days ...

[haesleinhuepf]

Maybe compare https://scikit-image.org/docs/stable/api/skimage.transform.html#skimage.transform.rescale instead of/and cle.scale.