Add demonstration GIF to readme

To motivate potential users

Author: tomlankhorst

README.md

@@ -8,6 +8,8 @@ OCS2 is a C++ toolbox tailored for Optimal Control for Switched Systems (OCS2).
 * SQP: Multiple-shooting algorithm based on HPIPM
 * PISOC: Path integral stochatic optimal control
 
+![legged-robot](https://leggedrobotics.github.io/ocs2/_static/gif/legged_robot.gif)
+
 OCS2 handles general path constraints through Augmented Lagrangian or relaxed barrier methods. To facilitate the application of OCS2 in robotic tasks, it provides the user with additional tools to set up the system dynamics (such as kinematic or dynamic models) and cost/constraints (such as self-collision avoidance and end-effector tracking) from a URDF model. The library also provides an automatic differentiation tool to calculate derivatives of the system dynamics, constraints, and cost. To facilitate its deployment on robotic platforms, the OCS2 provides tools for ROS interfaces. The toolbox’s efficient and numerically stable implementations in conjunction with its user-friendly interface have paved the way for employing it on numerous robotic applications with limited onboard computation power.
 
 For more information refer to the project's [Documentation Page](https://leggedrobotics.github.io/ocs2/)