Add CNAME file with custom domain

[tobil4sk]

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[tobil4sk]

There seems to be conflicting information in the docs about whether this is necessary:

https://docs.github.com/en/pages/configuring-a-custom-domain-for-your-github-pages-site/troubleshooting-custom-domains-and-github-pages#cname-errors

If you are publishing from a custom GitHub Actions workflow, any CNAME file is ignored and is not required.

https://docs.github.com/en/pages/configuring-a-custom-domain-for-your-github-pages-site/managing-a-custom-domain-for-your-github-pages-site#configuring-an-apex-domain

If you are publishing your site with a custom GitHub Actions workflow, no CNAME file is created, so you need to create one manually (containing only a line of text with your custom domain).

I asked to clarify here: github/docs#32930 (comment)