Added first version of the README file

README.md

+Example robot URDFs
+===============================================
+
+## <img align="center" height="20" src="https://i.imgur.com/vAYeCzC.png"/> Introduction
+
+This repository includes a set of robot descriptions that are aimed to be used in benchmarking. These source files do not intend to substitute original their repositories.
+
+**Authors:** Carlos Mastalli <br />
+**With additional support from the Gepetto team at LAAS-CNRS.**