doc/dev/Architecture.md can be (and is) out of date

I don't think this is a big problem, but it might be nice to improve this situation.

We could decide just to leave it as is, in which case we should probably put a note in saying it's historical.

OTOH we could decide to advertise this more to new contributors, and add the crates that we've added since, and add a CI job to check that published crates are mentioned in the file.