I'm a beginner. I'm using ros 2 - foxy and turtlebot3 burger. I follow the turtlebot3 manual and I get a map (map.yaml and map.pgm) after run slam simualation. I want to implement a complete coverage path planner. So first, i have to divide my map into many little cells (grid map) and visualize this grid map in rviz2. I have read gridmap package document https://github.com/ANYbotics/grid_map. From the gridmap package document, I found the "gridmaploader" package, but I don't know how to use that package to load my map.