Update README.md

- Add sentences clarifying users should include ".xml" extension on their sitemap name and why.
- Remove sentence from README about future possible addition of image & video sitemap extensions; both are deprecated by Google.

README.md

@@ -68,10 +68,6 @@
   ignore `lastmod` anyway since they only respect if it's ["consistently and
   verifiably
   accurate"](https://developers.google.com/search/docs/crawling-indexing/sitemaps/build-sitemap#additional-notes-about-xml-sitemaps).
-- [Image](https://developers.google.com/search/docs/crawling-indexing/sitemaps/image-sitemaps)
-  or
-  [video](https://developers.google.com/search/docs/crawling-indexing/sitemaps/video-sitemaps)
-  sitemap extensions.
 
 ## Installation
 
@@ -114,6 +110,8 @@ export const GET: RequestHandler = async () => {
 };
 ```
 
+Always include the `.xml` extension on your sitemap route name–e.g. `sitemap.xml`. This ensures your web server always sends the correct `application/xml` content type even if you decide to prerender your sitemap to static files. 
+
 ## The "everything" example
 
 All aspects of the below example are optional, except for `origin` and