Add new lines between refs

Signed-off-by: Addisu Z. Taddese <addisu@openrobotics.org>

Author: azeey

tutorials/lander.md

@@ -10,10 +10,15 @@ to the surface while they collect sensor measurements.
 ## Related tutorials
 
 \ref create_vehicle
+
 \ref adding_visuals
+
 \ref frame_reference
+
 \ref adding_system_plugins
+
 \ref theory_buoyancy
+
 \ref theory_hydrodynamics
 
 # Create your vehicle

tutorials/surface_vehicles.md

@@ -9,9 +9,13 @@ with the presence of waves and wind.
 ## Related tutorials
 
 \ref create_vehicle
+
 \ref adding_visuals
+
 \ref frame_reference
+
 \ref adding_system_plugins
+
 \ref theory_hydrodynamics
 
 # Adding an environment

tutorials/underwater_vehicles.md

@@ -12,10 +12,15 @@ guide you through the setup of the [MBARI LRAUV](https://app.gazebosim.org/accur
 ## Related tutorials
 
 \ref create_vehicle
+
 \ref adding_visuals
+
 \ref frame_reference
+
 \ref adding_system_plugins
+
 \ref theory_buoyancy
+
 \ref theory_hydrodynamics
 
 # Create your vehicle