Shuffle the README a bit.

I'm real impatient with READMEs. I want the first few paragraphs to
explain why I should care or, uh, I won't. I've tried to do that here.

I didn't keep the same tone. I'm not a super talented writer. Or, if I
am, I'm talented like a surgeon with a sledgehammer is talented.

Signed-off-by: Brian L. Troutwine <brian.troutwine@adroll.com>