Link architecture docs to modular reference example

Author: billybox1926-jpg

docs/ARCHITECTURE.md

@@ -4,6 +4,8 @@ This repository is a reusable template, so the architecture intentionally define
 
 Use these folders as stable seams for future projects. Keep implementation code small, composable, and easy to replace.
 
+For a tiny dependency-free walkthrough of the intended `core -> providers -> plugins` pattern, see `docs/examples/MODULAR_REFERENCE.md`.
+
 ## Layout
 
 ```text