title: Setting up custom https sub domains with github pages?
body: <p>If we want the custom domain <code>example.com</code> with our github pages, then we just go into settings and add <code>example.com</code>, and assuming that we have already added the A records for <code>@</code> to our domain name registrar this just works IIUC. </p>
  
  <p>Now if we also want a subdomain <code>sub.example.com</code> for another github repository do we enter <code>sub.example.com</code> in the repository settings panel for the custom domain? I assume this is all we have to do, assuming the A records for <code>sub</code> have already been setup?</p>
  
  <p>I've tried it out and post doing it I get this github message:</p>
  
  <blockquote>
    <p>Your site's DNS settings are using a custom subdomain, sub.example.com, that's set up as an A record. We recommend you change this to a CNAME record pointing at [YOUR USERNAME].github.io. For more information, see <a href="https://help.github.com/articles/setting-up-a-custom-domain-with-github-pages/" rel="nofollow noreferrer">https://help.github.com/articles/setting-up-a-custom-domain-with-github-pages/</a>.</p>
  </blockquote>
  
  <p>Why is github recommending this?  There is a reference URL included in the message, but it's a link to generic instructions on how to setup github custom domains, and there's nothing specific with respect to sub domains.</p>