New  multi-volume example (#169)
New  multi-volume example (#169)

* Create multi-volume.ipynb
multivolume example using PET-CT medical image (might make more sense than a head and astronomy image) it could also be taken one step further to be PET+CT+Label but that is harder to view

* Update multi-volume.ipynb

adding labels to multivolume (3 volumes), changing to MIP

maartenbreddels/ipyvolume,maartenbreddels/ipyvolume,maartenbreddels/ipyvolume,maartenbreddels/ipyvolume