Tested on OpenBSD 6.3 and macOS 10.13
Generate a new SSH key pair and copy public key to the clipboard.
$ xclip -selection clipboad ~/.ssh/id_ed25519.pub $
Open your GitHub profile.
On Personal Settings > SSH and GPG keys page click New SSH key.
Type-in a Title, for example, a hostname of your computer.
Paste your public key into Key textarea.
Click Add SSH key.
Expect email A new public key was added to your account from GitHub.
$ ssh -T firstname.lastname@example.org Hi romanzolotarev! You've successfully authenticated, but GitHub does not provide shell access. $
GitHub makes your public key available via HTTPS.
$ curl https://github.com/romanzolotarev.keys ssh-ed25519 AAAAC3NzaC... $