Determine and document supported Python versions

[sadielbartholomew]

Using Python 3.8, I can run cf-view fine, but with 3.12 I get the error of:

$ cfview                                                          ─╯
Traceback (most recent call last):
  File "/home/slb93/miniconda3/envs/cf-env-312/bin/cfview", line 27, in <module>
    from PIL.ImageQt import ImageQt
ImportError: cannot import name 'ImageQt' from 'PIL.ImageQt' (/home/slb93/miniconda3/envs/cf-env-312/lib/python3.12/site-packages/PIL/ImageQt.py). Did you mean: 'Image'?

so there are clearly Python versions, not just older but also newer, for which cf-view doesn't currently work. These are not currently documented as far as I have seen, so we should find out which versions are supported so that cf-view runs, and clearly specify these, including enforcing as a packaging requirement.