doc: add note about ascii doc and demo project

Author: jknack

docs/asciidoc/modules/openapi.adoc

@@ -9,6 +9,9 @@ This library supports:
 - https://swagger.io/specification[OpenAPI 3] (json and yaml)
 - https://swagger.io/tools/swagger-ui[Swagger UI] (Optional)
 - https://github.com/Redocly/redoc[Redoc] (Optional)
+- AsciiDoc Output (Optional)
+
+Checkout the [demo project](https://github.com/jooby-project/library-demo)
 
 === Configuration
 
@@ -201,6 +204,8 @@ properties filter routes by their path pattern. The filter is a regular expressi
 
 === Documenting your API
 
+Full/complete example available [here](https://github.com/jooby-project/library-demo)
+
 ==== JavaDoc comments
 
 JavaDoc comments are supported on Java in script and MVC routes.