Add "Tell Git who you are" section

[allentiak]

There is no reference to the initial user and email setup (telling Git who you are):

$git config --global user.name "Your Name"
$git config --global user.email "your_email@example.com"

This node should be between "setup" and "create a new repository"

[ryanmjacobs]

I just added this in pull request #92.