To setup the model, first install and run Gazebo once, and then run the following script:
$ cd jetbot_ros/gazebo # substitute where you have jetbot_ros repo on your machine
$ ./install_jetbot_model.sh
The jetbot
model will then be symbolically linked to ~/.gazebo/models
and can then be loaded with Gazebo.
note: to uninstall the model, run
rm ~/.gazebo/models/jetbot