update readme

Author: cflinto

readme.md

@@ -8,6 +8,12 @@ camera perspective using ray-plane intersections and camera modeling. It feature
 - A command-line interface for estimating object sizes from user input
 - Unit tests to verify the implementation
 
+The `core` folder contains all the logic related to the geometric size estimation,
+while the rest of the project is dedicated to providing utility/test scripts to use it.
+Most user should only use the `cli` folder to estimate object sizes from the command line
+or the `fps_demo` folder to visualize and interact in an fps-like environment (instructions below).
+Advanced user might create custom scripts that leverage functions from the `core` folder.
+
 ---
 
 ## Examples