Make explicit that the project builds on ROS

[jf---]

it would be welcome that the README.md makes the implementation explicit (that its using ROS) this is non-obvious since ABB controller support a REST API via webservices

Perhaps the best way would be to render the diagram (https://github.com/compas-rrc/compas_rrc/blob/main/images/overview-diagram.png) in the README.md? It's gorgeous and the architecture of the project is crystal clear