Update .changeset/weak-dancers-beam.md

Co-authored-by: Sarah Rainsberger <[email protected]>

.changeset/weak-dancers-beam.md

@@ -2,4 +2,19 @@
 '@astrojs/vercel': minor
 ---
 
-Deprecate the functionPerRoute option
+Deprecates the `functionPerRoute` option
+
+This option is now deprecated, and will be removed entirely in Astro v5.0. We suggest removing this option from your configuration as soon as you are able to:
+
+```diff
+import { defineConfig } from 'astro/config';
+import vercel from '@astrojs/vercel/serverless';
+
+export default defineConfig({
+  // ...
+  output: 'server',
+  adapter: vercel({
+-     functionPerRoute: true,
+  }),
+});
+```