Fix typos in collision avoidance demo

[tickelton]

Fixes multiple typos in the collision avoidance demo:

• Readme says to open notebook in road_following directory; should be collision_avoidance instead
• live_demo_resnet18_build_trt.ipynb says to open live_demo_resnet18_build_trt.ipynb next which should be live_demo_resnet18_trt.ipynb