ROS: use TurtleBot3 robot simulator

Clone TurtleBot3 msgs:

git clone https://github.com/ROBOTIS-GIT/turtlebot3_msgs.git

Clone TurtleBot3 repo:

git clone https://github.com/ROBOTIS-GIT/turtlebot3.git

Set Turtlebot model:

export TURTLEBOT3_MODEL=burger

Add TurtleBot3 gazebo for simulation without a real robot:

git clone https://github.com/ROBOTIS-GIT/turtlebot3_simulations.git