docs(openapi): add External Resources section

docs/rest-api/openapi.yml

@@ -5,6 +5,14 @@ info:
     # Description
     This API documentation regarding OpenAPI specification. Generated by [ReDoc](https://github.com/Rebilly/ReDoc).
 
+    # External Resources
+
+    || URL |
+    | --- | --- |
+    | Website | https://yoshinorin.github.io/qualtet/docs/ |
+    | Source Code | https://github.com/yoshinorin/qualte |
+    | Response Examples | https://github.com/yoshinorin/qualtet-mock/tree/master/src/resources |
+
     # Common Headers
 
     ## Request Header
@@ -18,10 +26,6 @@ info:
     | X-Request-Id | UUID4 | Always set by Qualtet. If client set this when request a server, Qualtet will return it value with response header. |
     | X-Response-Time | number | Always set by Qualtet. Response time (ms) |
   version: v2.11.0
-externalDocs:
-  description: |
-    - Website
-  url: 'https://yoshinorin.github.io/qualtet/docs/'
 servers:
   - url: http://example.com/
 paths: