Add design-rules.md: use the catalog as an anti-slop rules file

README.md

@@ -6,6 +6,10 @@ None of these signs proves anything on its own. Almost every pattern here was in
 
 Contributions welcome. See [CONTRIBUTING.md](CONTRIBUTING.md). Content is licensed [CC BY-SA 4.0](LICENSE): copy it, translate it, build tools on it.
 
+## Use it as a design rules file
+
+This guide reads in two directions. As a detector, it tells you what to look for. As a rules file, it tells your coding agent what to design against, so your own project stops converging on the same defaults. Drop [design-rules.md](design-rules.md) into your project as `CLAUDE.md`, `.cursorrules`, or `AGENTS.md`, or paste it into a system prompt. It is written as "prefer a real decision over the reflex," not a blanket ban, because most of these patterns are legitimate in the right context. The point is to make the choice deliberate instead of default.
+
 ## Contents
 
 - [How to use this guide](#how-to-use-this-guide)