the "streams" exercise needs more details and hints

people new to hapi are likely not to be Node experts, and thus entirely likely to never have worked with streams and the `.pipe()` function before.

While the hints do cover how to create a stream, it does not cover how the rot13-transform library is supposed to be used in conjunction with streams, nor is a link provided for reading the API for this library, making "doing the assignment" more of a "hunt for other tutorials to explain how to use streams and the indicated library".

It would be a good idea to at least explain how to use streams with `.pipe()` and what not to do when you do read up on streams (e.g. don't end with a `pipe(process.stdout)`, which you might be tempted to do when you read https://www.npmjs.com/package/rot13-transform in order to find out how to use it, because Hapi will be adding more pipes)