Remember to change the path in ranger_mini_gazebo.xacro (for humble branch)

[Grange007]

I found the path to ranger_mini_joint.yaml is given in absolute path (as the picture shows, /home/agilex/ugv_sim/src/ranger_mini/config/ranger_mini_joint.yaml), which may cause some unexpected questions. For me, I encountered "Controller manager not available" when I wanted to launch the gazebo simulation for ranger_mini. I believe it is necessary to mention people (maybe in README) to change the path in ranger_mini_gazebo.xacro.