Make the code usable for computers without cuda

[pjpollot]

• Send to an optimal device if cuda is not dete (might be mps for M* chip Mac users).
• Add optional arguments for demo.py script: input and output given specific paths.
• Update README.
• A few minor changes.

[pjpollot]

Hi @Hzzone

I have slightly changed your repo to be usable for non-cuda devices (I tested my solution on a Mac with the M3 chip).
Please take a look to my modifications whenever you have time.

Kind,
Pierre