Create 2fa_checker.rb

We provide a UI way of saying "this user doesn't have 2FA on for the org":

![](https://cloud.githubusercontent.com/assets/83539/3900068/15ae444c-2285-11e4-9a0f-a4bcf6919fef.png)

But this is cumbersome to check. Let's provide a simple script to fetch this info.

/cc @github/api @github/docs-platform