Update README (#470)

Author: n-rodriguez

README.md

@@ -18,8 +18,8 @@ Sitemaps adhere to the [Sitemap 0.9 protocol][sitemap_protocol] specification.
 * Ensures your old sitemaps stay in place if the new sitemap fails to generate
 * Gives you complete control over your sitemap contents and naming scheme
 * Intelligent sitemap indexing
-* Compatible with Ruby from version 2.6 to version 3.4
-* Compatible with Rails from version 6.0 to version 8.0
+* Compatible with Ruby from version 2.6 to version 4.0
+* Compatible with Rails from version 6.0 to version 8.1
 
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