lacking of straightforward example

Hi there, 

Thanks for all, it works wonderfully.

I think it would be great to put a really easy example at the top of your README for clarity.

Following example might be obvious for everyone, but it  wasn't for me:

```
$ echo '{"token":"1234"}'  | jsawk 'return this.token'
1234
```

(feel free to close this issue if you want)
