Should probably add an instruction to add an import on P10

[brianwang9100]

Right before we get into the KeyboardNotificationHandler code, I'd recommend adding an instruction to add an import

import ConvenienceKit

When doing this tutorial it kinda confused me why I was getting errors for KeyboardNotificationHandler, and I'm assuming there are probably tons of beginners who run in to the same problem but don't know how to fix it.

I don't want to make a pull request cause I'm afraid i'll mess with the .md parser syntax, but if you want me to do so I can go ahead and put one in (kinda have a general idea of how the syntax works).