add comment for stopping the simulation

Bipedal/bipedal_planner/bipedal_planner.py

@@ -111,6 +111,7 @@ class BipedalPlanner(object):
                     if c > len(com_trajectory_for_plot):
                         # set up plotter
                         plt.cla()
+                        # for stopping simulation with the esc key.
                         plt.gcf().canvas.mpl_connect('key_release_event',
                                 lambda event: [exit(0) if event.key == 'escape' else None])
                         ax.set_zlim(0, z_c * 2)