Revise Unity environment model download instructions

Updated instructions for downloading and unzipping Unity environment models, including details on file structure and GPU recommendations.

Author: alexlin2

README.md

@@ -187,10 +187,22 @@ ros2 run pct_planner pcd_to_tomogram.py /home/user/maps/warehouse/map.pcd -o /ho
 
 The stack supports Unity-based simulation environments. Download a Unity environment model and unzip to:
 
-`src/base_autonomy/vehicle_simulator/mesh/unity/`
-
-Unity model download: `https://drive.google.com/drive/folders/1G1JYkccvoSlxyySuTlPfvmrWoJUO8oSs?usp=sharing`
-
+Download a [Unity environment model for the Mecanum wheel platform](https://drive.google.com/drive/folders/1G1JYkccvoSlxyySuTlPfvmrWoJUO8oSs?usp=sharing) and unzip the files to the 'src/base_autonomy/vehicle_simulator/mesh/unity' folder. The environment model files should look like below. For computers without a powerful GPU, please try the 'without_360_camera' version for a higher rendering rate.
+
+mesh/<br>
+&nbsp;&nbsp;&nbsp;&nbsp;unity/<br>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;environment/<br>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Model_Data/ (multiple files in the folder)<br>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Model.x86_64<br>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;UnityPlayer.so<br>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;AssetList.csv (generated at runtime)<br>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Dimensions.csv<br>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Categories.csv<br>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;map.ply<br>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;object_list.txt<br>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;traversable_area.ply<br>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;map.jpg<br>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;render.jpg<br>
 #### Base autonomy (simulation)
 
 ```bash