Hello, you would just need to create your contours in your program of choice (in the same coordinate system as your data). CAD or directly in the software you used to create the point cloud then export it as a .shp file which Potree can use. Upload the .shp file to your web server then use the appropriate code to bring it into your page. I wont have time to create a dedicated tutorial on this anytime soon but there are a lot of examples online of people doing this. Good luck!