Yea, I was caught off guard to see there's a Get Windows 10 icon sitting next to my clock this morning (especially on a corporate PC which wasn't eligible for the free upgrade, at in what they had previously explained.)
I don't have a test machine to play around with it, but it sounds better than Windows 8.1 and that's all I really want.
You can put it anywhere before the closing body tag - we happen to have it in the header because that was the best place for us to put it given the way we create page layouts. I would suggest you only put it in ONCE, though.