You must read this entire page before using your GitHub authorization code at the bottom.
It contains specific disclaimers about using the Handmade Hero GitHub that you will be affirmatively agreeing to by authorizing your username to access the private repository.
Q: 
What is this page for?
In response to overwhelming demand, we have created a private GitHub to host a copy of the Handmade Hero source code and a number of viewer-contributed ports to various platforms and languages. With your pre-order of Handmade Hero comes one activation code with which you can add your GitHub username to the private Handmade Hero GitHub.
Q: 
Is this a supported feature of Handmade Hero?
No, NO, and DOUBLE NO. This is strictly a bonus feature that we are providing as a thank-you. We do not guarantee that you can get access to the GitHub, and it is not part of the Handmade Hero pre-order. So if you give your access code to somebody, or use it to authorize the wrong username, we can’t help you. It’s gone. You’d have to buy another copy of Handmade Hero if you want another one. There is literally no support for this feature whatsoever.
Q: 
Where do I find my authorization code?
It’s on the SendOwl download page you received when you pre-ordered Handmade Hero (and where you normally download the source code ZIPs and asset files). You should see the code listed there next to the handmade_hero_git.txt download link.
Q: 
Where do I get a GitHub username?
This page assumes you already have one, which most people who want access probably do. But if you’ve never used GitHub before, then you need to register one here first to get a username. It’s free. Once you have the username, you can use your authorization code on to grant that username access the Handmade Hero repository using the form above.
Q: 
Do you monitor the contents of the GitHub?
We do not monitor the contents of the GitHub. You are responsible for looking at the contents and using them appropriately, and you do so entirely at your own risk. If someone posts an executable up there that steals your credit card information and formats your hard drive, don’t blame us, we had absolutely nothing to do with it.
Q: 
What happens to code I contribute to the GitHub repository?
Any code you contribute to the repositories will eventually be placed into the public domain along with the Handmade Hero source code on a date no later than two years from the final ship date of Handmade Hero. By contributing code, you implicitly agree to that eventuality. If you want to keep your copyright, please do not contribute to the community-maintained respositories! Keep the code to yourself, or use your own private branch of the Handmade Hero source instead, which is something GitHub supposedly makes very easy to do.
By entering your GitHub username and authorization code below and hitting “authorize”, you’re agreeing to abide by these terms.
If that’s all OK with you, have at it: