Instead of "redirect the root domain to the www subdomain using a DNS CNAME record" it should say "... using domain forwarding".

Most DNS hosts offer some mechanism for forwarding traffic from your apex domain to the www subdomain using a 301 (permanent) redirect. Then the www subdomain can be configured with a CNAME record.

For example, at Brace (http://brace.io) we offer a guide for configuring this if your domain is on godaddy. See step 3 at http://blog.brace.io/2014/01/19/custom-domains-godaddy/. (not an endorsement of godaddy)

(edited for clarity)