Add MPS support for Gradio demo

[fakerybakery]

Hi, Thank you for creating this amazing software. Looking forward to the license change (#16)!

This PR adds support for Apple Silicon (M1, M2, M3, etc) GPU devices (on arm64 Macs) using MPS.

However, there are some limitations on Apple Silicon devices. Please see the modified README for details:

Apple Silicon (MPS) GPUs are partially supported, however not all operations are available due to the lack of complete MPS support in PyTorch.

Until full MPS support has been added to PyTorch, please prepend all your commands with:

PYTORCH_ENABLE_MPS_FALLBACK=1 python ***.py

Or, in Python:

import os
os.environ["PYTORCH_ENABLE_MPS_FALLBACK"] = "1"

Please let me know if you have any questions or comments!