add loguru to requirements.txt

[surcyf123]

https://github.com/opentensor/bittensor-subnet-template/blob/332a4177b6ad85fcf421600758618d9bc4a8b207/template/utils/config.py#L23

This import imports from loguru, yet when you install the repo, loguru does not get installed as it's not in the requirements.txt file.