Describe Project Structure

[JLambertazzo]

Currently it is unclear where to make contributions/changes. Need an outline of the project to be added to either README.md or CONTRIBUTING.md. The outline is something like the following:

Core Library & Logic -> /lib/ folder
Website -> HTML in root
-> styles in /css/ folder
-> scripts in /js/ folder

list-extender folder should be removed soon

[maple0311]

@JLambertazzo Please assign this to me, under hactoberfest 2023 accepted label.