sphinx-doc.org APAX domain setting for ReadTheDocs

[shimizukawa]

We previously did DNS configuration for HTTPS on www.sphinx-doc.org on #5522 (Fall 2018).

At the time, the official ReadTheDocs documentation stated that "ReadTheDocs doesn't support naked domains.", but now it states that they can be configured with ANAME.

https://docs.readthedocs.io/en/stable/custom-domains.html

For a subdomain like docs.example.com add a CNAME record, and for a root domain like example.com use an ANAME or ALIAS record. (it comes since https://github.com/readthedocs/readthedocs.org/pull/9266, maybe)

Also, on 8/30/2022, ReadTheDocs sent an email notification to me, noting that the sphinx-doc.org domain was not set up correctly.

This ticket will do the following.

• Add DNS record: sphinx-doc.org. ANAME www.sphinx-doc.org.

This will solve two problems.

• https://sphinx-doc.org was not being provided.
• ReadTheDocs alerts are being displayed for sphinx-doc.org.