Architecture.md is urging open-source project maintainers to include an ARCHITECTURE document alongside README and CONTRIBUTING files for projects between 10k-200k lines of code. The document should describe the high-level project architecture in a concise manner. This document helps contributors understand the project structure, reducing the time it takes to make a patch. It emphasizes not getting too detailed to avoid constant updates. It suggests including a codemap with coarse-grained modules and architectural invariants, and emphasizing boundaries between layers and systems. The ARCHITECTURE document should be revisited periodically and kept separate from code, to provide a roadmap for contributors and maintainers.
https://matklad.github.io/2021/02/06/ARCHITECTURE.md.html