clarifies instructions in proxy challenge 

Also added a wikipedia link for complete beginners to read up on proxies and hapi's reply.proxy() ref.
Let me know if this is too much. Thanks.

99% of developers have never written a proxy.
most beginners do not know what a proxy *is*. 
the wikipedia link was to help *beginners*...
of the [605](https://www.npmjs.com/package/makemehapi) people who have downloaded **makemehapi** this month, do you have stats for how many of them *completed* the tutorials...?

I've sat with *** complete beginners*** at [Nodeschool](http://nodeschool.io) events, [Founders & Coders](http://foundersandcoders.org/#/aboutusteam) / [Makers Academy](http://www.makersacademy.com) drop-in sessions and people ask:
> "**What is a *Proxy***"  
*All the time...*

If you don't want to bloat the instructions, fair enough, but for someone trying this tutorial on their own, some guidance is *pivotal*. Sure, they can just *Google* for it, but this is the first result that comes up when I google: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Proxy which is *seriously confusing* to a beginner.

@nvcexploder I started writing a [Lab](https://github.com/hapijs/lab) "Level" for **makemehapi** but when I saw how difficult it was to get a PR merged for a simple copy change I gave up on the idea. I *love* Hapi, but there appears to be a lack of [**Shoshin**](http://en.wikipedia.org/wiki/Shoshin) here... :broken_heart: