help of native function should return something

If you call `help` on JavaScript function, it should do something like short message that only lips functions have docs.

e.g.:

```scheme
(help setTimeout)
;; ==> "this is a native function, no docs available"
```

Start at the implementation of the `help` entry point and trace how `(help setTimeout)` handles a native JavaScript function. Check whether existing help-related tests cover functions without documentation; done means native functions return a short, consistent message rather than producing no result.

Written by the indexing model from the issue text.