add schema as image in readme

[vincentsarago]

source: https://gist.githubusercontent.com/vincentsarago/e945d27cd8494a353197639f564e8372/raw/d9cc45ab4b81dc6ba5b95d4e7a407dd95201c8cd/Untitled-2021-05-03-1148.excalidraw

made with https://excalidraw.com