lab2.md

@@ -222,6 +222,8 @@ Modify the publisher example to instead publish a ```geometry_msgs/msg/Twist```
 
 The documentation for ```geometry_msgs/Twist``` can be found online at [geometry_msgs/Twist](https://docs.ros.org/en/api/geometry_msgs/html/msg/Twist.html) or by running ```ros2 msg info geometry_msgs/Twist```.
 
+Notice that for the Turtlebot 4 we must rotate to the direction we want to move.  That means that if the robot is pointing in the x direction and we do not give any angular speed around z-axis then if we only give linear speed in y the robot will not move since forward for the robot is in the x direction.
+
 Listening to a Topic
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