replaced external tutorial link with internal link

Author: john-chrosniak

tutorials/docs/navigation2_route_tool.rst

@@ -23,7 +23,7 @@ Prerequisites
 ============
 
 Prior to using the route tool, you will need to create an occupancy grid map using the slam_toolbox package. 
-Follow `this tutorial <https://roboticsbackend.com/ros2-nav2-generate-a-map-with-slam_toolbox/>`_ for instructions on how to generate and save an occupancy grid map.
+Follow `this tutorial <https://docs.nav2.org/tutorials/docs/navigation2_with_slam.html>`_ for instructions on how to generate and save an occupancy grid map.
 
 Tutorial Steps
 ==============