Update README.md

Updated README.md
The goal of this REAMDE is to teach other Prediction.IO user how to use this stock engine.

We can always assume that the user already has Prediction.IO and all its dependencies installed.

It is a nice act to remind user how to setup the infrastructure, but this instruction may change from time to time. Perhaps adding a link to the installation notes is an easier way.

http://docs.prediction.io/0.8.1/install/