docs: update cloudflare get started docs (#42)

Author: xiaoyu2er

pages/cloudflare/get-started.mdx

@@ -48,7 +48,7 @@ compatibility_date = "2024-09-23"
 compatibility_flags = ["nodejs_compat"]
 
 # The binding name must be "ASSETS" when the cache is enabled
-assets = { directory = ".worker-next/assets", binding = "ASSETS" }
+assets = { directory = ".open-next/assets", binding = "ASSETS" }
 ```
 
 <Callout>