doc(sitemap): improve filtering doc

docs/content/2.sitemap/2.guides/0.filtering-urls.md

@@ -56,14 +56,25 @@ export default defineNuxtConfig({
 })
 ```
 
-These can be regex or a string path.
+Either option supports either an array of strings, RegExp objects or a `{ regex: string }` object.
 
-It's important to know that when providing a string, you can't use variable path segments in front of static ones.
+Providing strings will use the [route rules path matching](https://nuxt.com/docs/guide/concepts/rendering#hybrid-rendering) which
+does not support variable path segments in front of static ones.
+
+For example, `/foo/**` will work but `/foo/**/bar` will not. To get around this you should use regex.
+
+### Regex Filtering
+
+Filtering using regex is more powerful and can be used to match more complex patterns. It's recommended to pass a 
+`RegExp` object explicitly.
 
 ```ts [nuxt.config.ts]
 export default defineNuxtConfig({
   sitemap: {
-    exclude: ['/**/secret-pages'], // this won't work
+    exclude: [
+      // exclude /foo/**/bar using regex
+      new RegExp('/foo/.*/bar')
+    ],
   }
 })
 ```