docs: restore OpenAPI and Postman links in README

Author: KikuAI-lab

reliapi/README.md

@@ -158,10 +158,10 @@ docker run -d -p 8000:8000 \
 ```
 
 ## Documentation
-- [GitHub Wiki](https://github.com/KikuAI-Lab/reliapi/wiki) - Complete documentation and guides
-
-
 
+- [OpenAPI Spec](./openapi/openapi.yaml) - Complete API specification
+- [Postman Collection](./postman/collection.json) - Import into Postman for testing
+- [GitHub Wiki](https://github.com/KikuAI-Lab/reliapi/wiki) - Complete documentation and guides
 - [Full Documentation](https://reliapi.kikuai.dev)
 
 ## License