Update docs: Yoast SEO News sitemap

[maybellyne]

Please give us a description of the issue

The default Yoast SEO News sitemap is at /news-sitemap.xml/. But when there's a CPT with the name News, the default Yoast SEO News sitemap becomes /yoast-news-sitemap.xml/ while the CPT sitemap becomes /news-sitemap.xml/. This should reflect in the documentation at https://developer.yoast.com/features/xml-sitemaps/functional-specification/#news-sitemaps

• I've read and understood the contribution guidelines.
• I've searched for any related issues and avoided creating a duplicate issue.