From the top:
For GithubCreate a directory on your mac to hold your sites locally - I called mine /pages.
Create a repository on github, it doesn't matter what it is named, but pick a name that will match your domain at some level.
Clone the github repository from your pages directory.
git clone email@example.com:github-username/repository-name.git
Go into that directory.
Create a new branch called "gh-pages". Use this command:
git checkout --orphan gh-pages
In this directory, create a text file named "CNAME". Put the url of the domain in it. That's the only content. Include the subdomain. For example: www.example.com
Create a file called "index.html". Just to have something there to see. Put whatever you like in it.
Commit and push this to github.
git add .
git commit -m 'First commit'
Just add another repository and follow the same path.
For your registrarAt your registrar, forward your Apex domain to a subdomain, like www. At godaddy, this was easy enough. Choose forwarding when managing your domain, choose 301 (permanent) and enter the entire host (www.example.com).
Edit the zone file - create a CNAME where the subdomain ('www' in this case), points to this domain:
Multiple domains?All domains hosted on github (if you have others) will have a CNAME in the zone file point to the same location at github.io.
Finished!Wait a little while - at godaddy is was only a couple seconds. At 101domain.com it took over 24 hours.
Whenever you push your site to github, you will see your updates.
One more thing
Forwarding emailThere was one more thing I wanted. I wanted an email at that domain to forward to my personal email. So I could temporarily use it and post it on the site.
In Godaddy, there is an easy enough way to forward email. I used these instructions. Note, you probably don't need to change the MX records. I didn't, I just created the forwarding email address and made it a "catch all".