Add additional help to the DNS configuration page

[mikelittle]

If someone looking to launch a site into production ends up at the DNS configuration page, it can be a little confusing when read out of context.

It would be good to reference the Launcing a site on Altis page.

It would also be useful to expand the reasoning behind the domain apex vs subdomain information.

It may be useful to add information about the potential downfall of using ANAME/ALIAS records. See https://bunny.net/blog/how-aname-dns-records-affect-cdn-routing/ for reference. This may not apply to Route53 hosted domains, so that should be noted too if it is the case.

Hat tip: @svandragt