Add proper documentation to PET-related classes #192
Description
What would you like changed/added and why?
There is a number of classes/functions that are missing proper docstrings in the PET-related classes, e.g. PETModel, data.petPET.set_transform, data.petPET.to_filename, etc.
The files added/modified in PR #174 should give an accurate idea of what functions need to be documented properly.
Do you have any interest in helping improve the documentation?
Yes
Do you have any suggestions for the new documents?
No response