Add breakout diagram to ECS chapter introduction

[alice-i-cecile]

Created by @doup here: #290 (comment)

If you want to tackle this, DM me and I can get you access to the source files.

[Weibye]

Does Zola support mermaid?

It seems to be able to if we follow this, but would mermaid be a good enough tool to display these kinds of diagrams?

I know the "no javascript in my browser" crowd would not be able to see them, and I'm not sure if there's any way to statically generate them as svgs ahead of time

[alice-i-cecile]

Mermaid would be super cool here, because of how much easier it would be to maintain.

I'm not sure the no-JS crowd is particularly passionate about introductory diagrams, and I'm generally not keen on prioritizing their preferences when there's real tradeoffs to be made.