chore(readme): use better example snippet for undocumented params

Author: stainless-app[bot]

README.md

@@ -279,9 +279,8 @@ parameter. This library doesn't validate at runtime that the request matches the
 send will be sent as-is.
 
 ```ts
-client.foo.create({
-  foo: 'my_param',
-  bar: 12,
+client.files.upload({
+  // ...
   // @ts-expect-error baz is not yet public
   baz: 'undocumented option',
 });