Doc confusion: no instance of the proposed Functor in "type lambda gotchas"

In Type Lambda gotchas:

> In these cases you should prefer the lambda syntax, which would be written as:
> 
> ```scala
> Functor[Lambda[a => Future[List[a]]]]
> ```

The documentation doesn't explicitly refer to Cats' `Functor`, but most people are going to assume that, and Cats provides no such functor out of the box.