Added ROS-on-EV3 to post for Project Gallery

Sharing my project with a HowTo get [ros/ros_comm](https://github.com/ros/ros_comm) on to an EV3 with ev3dev.

It's a work in progress but I cleaned up the HowTo last week to share it now as I know I won't have time to work on it again over the next several weeks. 


We originally intended "building instructions" to be a pdf of how to build the LEGO model that goes with your project, but :+1: on re-purposing the link.