Add Railiance overlay repo scaffold

tools/README_tools.md

@@ -59,4 +59,9 @@ This model emphasizes:
 
 ---
 
+### `create_railiance_overlay_repo.sh`
+- Scaffolds a local Railiance overlay repo for a third-party upstream app.
+- Records upstream identity without vendoring upstream code.
+- Generates `railiance/app.toml`, a thin chart, stage values, tests, and runbooks.
+
 ✦ Railiance is not just code — it’s a way of letting infrastructure **colonize new worlds**.