Improve Jupyter-Notebook Documentation

[tibuch]

The information about the number of epochs used for proper training should be highlighted (red and large font).

In the 3D example we should additionally explain that more training-epochs could significantly improve the result.

[fjug]

Lovely! Additionally we should also notify people doing multi-channel data. Plus: it would be nice to test if the undertrained halo-issue become less pronounced on isotropic data. (A good picture in my mind is that a z-stack with massive \delta z is essentially the same as multiple channels between which changes are typically also not smoothly changing. Does this make sense? (No need to comment if it does...)