docs(config): Add warning on config in promise usage (#2890)

* Add warning on config in promise usage

* Update src/content/configuration/configuration-types.md

Co-Authored-By: Eugene Hlushko <jhlushko@gmail.com>

Author: 2 people

src/content/configuration/configuration-types.md

@@ -62,6 +62,8 @@ module.exports = () => {
 };
 ```
 
+W> Returning a `Promise` only works when using webpack via CLI. [`webpack()`](/api/node/#webpack) expects an object.
+
 
 ## Exporting multiple configurations