add missing ros2 launch cmd

nav2_gps_waypoint_follower_demo/README.md

@@ -4,7 +4,7 @@ A tutorial package provided in `navigation2_tutorials` to showcase the usage of
 `FollowGPSWaypoints` is an action interface in `nav2_waypoint_follower`, which directly accepts GPS(lat,long,alt) waypoints and navigates robot through them. You can see the Readme page of `nav2_waypoint_follower` package for more details of this action but 
 in a glance, we can summarize this as: 
 `robot_localization`'s `navsat_transform_node` provides a service named `fromLL`, which is used to convert pure GPS coordinates(longitude, latitude, alitude)
-to cartesian coordinates in map frame(x,y), then the existent Follow Waypoints logic from `nav2_waypoint_follower` is used to get robot go through each converted waypoints. Finally this process is exposed as `FollowGPSWaypoins`. 
+to cartesian coordinates in map frame(x,y), then the existent Follow Waypoints logic from `nav2_waypoint_follower` is used to get robot go through each converted waypoints. Finally this process is exposed as `FollowGPSWaypoins` action. 
 
 This package includes a sample Gazebo world that was used to collect GPS waypoints. You can collect GPS waypoints given that your robot is attached with an GPS sensor that provides (lat,long,alt). Then you can subscribe to the GPS topic and save the waypoints to YAML file given in `params` folder of this package. 
 e.g `ros2 topic echo /gps/fix`. 
@@ -28,6 +28,9 @@ Fist you need to make sure `GAZEBO_MODEL_PATH` IS set such that the specifc mode
 ```bash
 export GAZEBO_MODEL_PATH=$GAZEBO_MODEL_PATH:/home/YOUR_USER_NAME/colcon_ws_rolling/src/navigation2_tutorials/nav2_gps_waypoint_follower_demo/models
 ```
+```bash
+ros2 launch nav2_gps_waypoint_follower_demo city_world.launch.py
+```
 The above command should start gazebo world, at this point you should figure out a way to spawn your robot into that world.
 
 ## Request waypoint following