Enums, error messages

Hi,  just a question. 

When the framework is unable to parse enums, wouldn't it make sense to list what the valid values are? 

```diff
-- Argument 'fruit' failed to parse, provided value: Potato
++ Argument 'fruit' is invalid. Provided value: Potato. Valid values: Orange, Grape, Apple
```



```cs
ConsoleApp.Run(args, (Fruit fruit) => { });

enum Fruit
{
    Orange, Grape, Apple
}
```

