Update installation doc regarding Github API configuration

[vulongphan]

Fixes #1679

I have verified that this pull request:

• has no linting errors (npm run lint)
• is from a uniquely-named feature branch and has been rebased on top of the latest develop branch. (If I was asked to make more changes, I have made sure to rebase onto develop then too)
• is descriptively named and links to an issue number, i.e. Fixes #123

[vulongphan]

@catarak I have committed new changes based on your requested changes. Could you please have a look to make sure the documentation is clear and adequate?

[catarak]

Thanks for incorporating the changes! I think you should link to the GitHub API Section from the installation steps rather than the other way around—I think it will be more clear to someone going through the installation for the first time!

[vulongphan]

Yeah, it makes sense to me too, this way it is easier to navigate for someone going through the documentation for the first time. I also updated the document according to this. Could you please check the most recent commit (id: d1f5de4) and tell me if it is okay?

[vulongphan]

@catarak sorry for the broken link, I have fixed it in my most recent commit.

[catarak]

Thank you for working on this! I updated the copy a little but more 😄