Replace GitHub instructions with links
Should we replace the subsections Fork Nixpkgs on Github to Create a pull request on GitHub with links to relevant pages on GitHub? Their documentation is probably better than something we would produce. And it'll stay up-to-date with changes on Github.
1. Join GitHub
2. Fork a repo
There are some nix specific parts that should still be kept in the article. Like how to build a package using the git repository from source and `Becoming a Nixpkgs maintainer`