Document architecture and specific technical choices

[achou11]

Our development docs have some documentation about the project structure but it would also be helpful to have some notes about specific technical choices that were made and why. Examples could include: libraries that are used extensively (for things like component library, state management, localization, and routing), build tooling, release management, etc.

Probably makes most sense to create a separate document for this stuff (something like ARCHITECTURE.md)