Please, move vincent.initialize_notebook() to the top of Vincent Quick Start

[rominf]

I've used Vincent (in IPython notebook) several months ago. To refresh my memory I've opened Quick Start, saw import and Line usage, remembered (almost) everything about this library, wrote this code into IPython notebook and... nothing. Results were empty. I had to spend 10 minutes with Firebug (is vega loading?) trying to understand the reason. Finally I reread Quick Start almost until the end and stumbled upon IPython integration.

I think that most users use Vincent in the IPython notebook. Please, move vincent.initialize_notebook() to the top of Vincent Quick Start, because people tend to copy paste code and expect that it would work, moreover it's presented as IPython notebook.