Updated README

* removed reference to ros-groovy-pr2-controllers-msgs (doesn't exist any more)
* rosinstall uses raw Github URL
* added some missing steps
* removed reference to urdf_tools (not needed any more at all, can be removed from .rosinstall)
Merge pull request #1 from mintar/patch-1

Updated README
removed reference to ros-groovy-pr2-controllers-msgs (doesn't exist any more)
rosinstall uses raw Github URL
added some missing steps
removed reference to urdf_tools (not needed any more at all, can be removed from .rosinstall)