Improve README w.r.t "ready"

Hopefully these changes will prevent other people getting confused because of a missing call to `ready` (see #23)

I've separated the changes into two commits so that you can choose whether you want to add the comment; although it does help to prevent this issue, you could also argue that the first code example that new users might see should focus on conciseness and elegance and not scare them off with gotchas. I'll leave it up to you.

(Also I'm not sure why the getAttr change is in there; my git-fu's not good enough to remove it... sorry!)