robots: document upstreams & license, fix #34 (#98)

robots/anymal_b_simple_description/README.md

robots/baxter_description/README.md

robots/bolt_description/README.md

robots/double_pendulum_description/README.md

robots/finger_edu_description/README.md

robots/hector_description/README.md

robots/hyq_description/README.md

robots/icub_description/README.md

robots/iris_description/README.md

robots/kinova_description/README.md

robots/panda_description/README.md

robots/romeo_description/README.md

robots/simple_humanoid_description/README.md

robots/solo_description/README.md

robots/talos_data/README.md

robots/tiago_description/README.md

robots/ur_description/README.md