Add openapi.json route documentation (strapi#2143)

Author: faessler

docusaurus/docs/dev-docs/plugins/documentation.md

@@ -10,7 +10,9 @@ The Documentation plugin is useful to document the available endpoints once you
 
 If installed, the Documentation plugin will inspect content types and routes found on all APIs in your project and any plugin specified in the configuration. The plugin will then programmatically generate documentation to match the [OpenAPI specification](https://swagger.io/specification/). The Documentation plugin generates the [paths objects](https://github.com/OAI/OpenAPI-Specification/blob/main/versions/3.1.0.md#paths-object) and [schema objects](https://github.com/OAI/OpenAPI-Specification/blob/main/versions/3.1.0.md#schema-object) and converts all Strapi types to [OpenAPI data types](https://swagger.io/docs/specification/data-models/data-types/).
 
-The generated documentation can be found in your application at the following path: `src/extensions/documentation/documentation/<version>/full_documentation.json`
+The generated documentation can be accessed either through your application's source code or through the running application itself:
+- **Source code**: The documentation is located at <br/>`src/extensions/documentation/documentation/<version>/full_documentation.json`
+- **Running application**: Use the URL <br/>`<server-url>:<server-port>/documentation/<version>/openapi.json`
 
 ## Installation