This repository is now archived as it hadn't gathered as much attention as I'd hoped :(
To get a cool subdomain for your own GitHub Pages site follow these easy steps:
If you haven't already, now it's time to log in to your GitHub account and set up your GitHub Pages site following the instructions here. To get a head start you can simply use the generator with one of the provided themes and add some reasonable content to your new page.
Now determine your codes.kiwi subdomain: either choose your username or the name of your repo according to the existing GitHub Pages URL (for http://foo.github.io/bar, either foo.codes.kiwi or bar.codes.kiwi would be possible).
Add a file named CNAME to your repo (in the gh-pages branch for project pages) with a single line matching the domain you have chosen (e.g. foo.codes.kiwi). If you prefer a web interface form, have a look at GitHub Pages Help.
To finish the procedure, make a pull request in this GitHub repository that adds your subdomain to the list of existing codes.kiwi domains. Your new URL should go live within 24 hours (keep an eye on your pull request in case of a naming conflict).
... to Cloudflare for providing the robust DNS service that makes this possible - for free too!