Improve formatting in README a bit
Improve formatting in README a bit

Fewer `code` blocks means fewer grey boxes.
zhangweiyu51/git-up,jeremywiebe/git-up,Borgaard/git-up,milosm/git-up,albfan/git-up,Loke155/git-up,aanand/git-up,bhalothia/git-up,christer155/git-up