Use a fine-grained Github token

[GustawXYZ]

Hey,
First of all this script is amazing. I dare say it's a full blown distro-installer :D

When I configured the Git Backup, I've noticed that you recommend a classic token, which has access to all repositories. I have just tried it with a fine grained-token, where I only specify it for the config repo and give it Contents Read and write. It worked fine, the repository got updated. So I think it would be good to update the instructions, since the git-backup only needs one repository.