update README with a how-to-use tutorial

[flynneva]

need to add instructions for people on how to run with rosbridge

[jaguardo]

I basically used this tutorial: https://msadowski.github.io/ros-web-tutorial-pt1/ to get me started with rosbridge, and then removed all the typical roslibjs calls and replaced them with react-ros calls to drive the turtle sim... the only piece really missing is a better feedback of the turtle position, need to find a quick/easy way to plot position... been looking at leaflet for another project, can get complex fast.