Repo url of fork

[pietroppeter]

When working with a repo where you commit directly html files, if someone forks your repo and commits an html, the repo url will be the repo of the fork. The fix should likely be to add a git_repository_url field to nimib.toml that can override the url automatically detected from git.

[pietroppeter]

see example of this issue here (first commit): pietroppeter/p5nim#6