Updated documentation about client code generation

README.md

@@ -15,3 +15,13 @@ npm run serve -- --watch
 Now open http://localhost:8080/. You should see the generated API doc.
 
 Make modifications to `doc/specs/lichess-api.yaml`, and reload the page to see your changes.
+
+## Auto-generate client code
+
+You may use the spec file to quickly auto-generate the client code needed to interface your software to the Lichess API.
+
+To do so, you shall use the [OpenAPI Generator](https://openapi-generator.tech).
+
+The generator does not yet support the 3.1 version of the OpenAPI specification ([see this issue](https://github.com/OpenAPITools/openapi-generator/issues/9083)), the one used by Lichess, hence for now you should use the `doc/specs/lichess-api-3.0.yaml` file with it.
+
+The 3.1 format slightly differs from the 3.0 format, however the generated code is equivalent.