docs: Update stale links in docs for contributing

[Lutherwaves]

It appears the CONTRIBUTING.md file has become a bit stale, as the links referenced have been removed/changed (post Microsoft acquisition of Github).

I am mostly raising the PR to address the issue of the guide not being held up to date. It would be good to have an up-to-date guide on how to contribute.

I also recommend the CONTRIBUTING Guide to be extended with some rules or links to requirements about commit messages, as well as PR/Issue description templates. Happy to assist with some suggestions on that as well subsequently.