feat: explanatory diagrams using d2

[xynydev]

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[github-actions]

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Preview deployment: https://d2-bluebuild-website.xyny.workers.dev/

[xynydev]

See the diagrams here: https://d2-bluebuild-website.xyny.workers.dev/learn/how/

I saw this tool, D2, and immediately thought "this would be a really good thing to integrate on the BlueBuild site so that we can diagram the architecture a bit". I thought the diagrams looked way better than those generated by any competitors. But the ones I was looking at were generated with TALA, their closed source and paid layout engine. Oh well... Better something than nothing, I guess. But we aint paying 3k a year for some diagrams.

I could turn these into beautiful handcrafted diagrams, but I'm not sure if the ideas are good enough yet. But, this page needs to be written, and it's not like these can make the page less readable, right?