Deid logging update

[shubham-s-agarwal]

This minor update is to document chunking (better) and add logging for it as well

[shubham-s-agarwal]

I feel we've covered all of it. Tom please let me know in case you feel we could add it anywhere else.

[tomolopolis]

fine without further debug statements. Adding debug elsewhere you see fit is up to you, but the Trainer callback also has the same purpose