Simple flowcharts and diagrams are a good way to explain concepts without a ton of words.
Technical documentation is a lot more interesting (and helpful) when you mix in some visuals.
I used to draw these kinds of things in Concepts on my iPad, but my handwriting sucks and there aren't very clean ways to save and revise drawings in the future, especially for someone besides myself. Figma is another option here, but for simple diagrams that often gives me too many options which pull me into "high-fidelity" mode and then I get stuck.
The limitations of Excalidraw are a feature, not a bug.
Here's an example that I used on dropseed/deps:
And here it is being used on the README:
The best part? There's a link to the drawing itself, commented out in the markdown:
<!-- Edit in Excalidraw: https://excalidraw.com/#json=6195990008692736,unm4UYeUzdmbXTk_xcvIdQ --> ![deps overview flowchart](https://user-images.githubusercontent.com/649496/111809843-675b1000-88a3-11eb-8b5c-d85d71cb5a25.png)
Anybody can open that Excalidraw link (including me), edit the drawing and contribute a new version to the README. No complicated software or design tools, and limited choices in fonts, colors, and style.