Document verified prototype overlay behavior

examples/library-adoption/README.md

@@ -36,6 +36,9 @@ from `profiles/`. An explicitly supplied `--proposal-profile` or
 requested overlay and each effective profile, backend, and model. Synthetic model
 IDs demonstrate operator-selected routing; they are not measurements of price,
 speed, or model quality.
+`overlays/` contains ConfigKit application-setting layers; `profiles/` contains
+PromptKit execution profiles. Profile paths resolve from the main `config.yaml`
+directory, including when an overlay is selected.
 An overlay can also change ordinary backend settings and credential references.
 ConfigKit resolves only the surviving reference at a replaced credential path;
 changing role profiles alone leaves other configured backend credential references