Detect GitHub Pages

[jayvdb]

e.g. #94 loads https://biopython.org/, which has header 'Server': 'github.com'.

That might be sufficient to find the GitHub Pages repository, which may help find the appropriate GitHub repo.

It might also trigger other SCM being negatively scored, as there is an expectation that the code repository would be found on GitHub. This could help with #6