The original song is surprisingly difficult to play. It requires some serious stretch for some of the chords. When I set out to write a fingerstyle guitar arrangement of this song for my students here in Vancouver, I decided to place it in open position, thus avoiding one of the very difficult stretches.
In fact, playing the original song in open position is possible -- almost -- it's just one chord that we're unable to play in open. Sometimes I let my students cheat and play the song in open but change that one chord pattern so it works out.
This acoustic guitar arrangement uses those open position shapes. If you want to match the original key you'll have to put a Capo on the first fret. Personally I don't think it matters, and I suggest you can just play it without a capo. In this arrangement we aren't singing anyway, so to put it down a half-step is no big deal.
Download a PDF of my arrangement here, or the images below will show you the whole thing.