doc: Add docs for UrlKeys

packages/docs/content/docs/batching.mdx

@@ -148,3 +148,24 @@ setCoordinates({
 })
 ```
 
+As your application grows, you may want to reuse these parsers and urlKeys
+definitions across multiple components or nuqs features
+(like [loaders](./server-side#loaders) or a [serializer](./utilities#serializer-helper)).
+
+You can use the `UrlKeys{:ts}` type helper for this:
+
+```ts
+// [!code word:UrlKeys]
+import { type UrlKeys } from 'nuqs' // or 'nuqs/server'
+
+export const coordinatesParsers = {
+  latitude: parseAsFloat.withDefault(45.18),
+  longitude: parseAsFloat.withDefault(5.72)
+}
+
+export const coordinatesUrlKeys: UrlKeys<typeof coordinatesParsers> = {
+  latitude: 'lat',
+  longitude: 'lng'
+}
+```
+