Add a lil bit more explanation of what is going on

Author: Luca Forstner

src/platforms/javascript/guides/nextjs/manual-setup.mdx

@@ -257,6 +257,8 @@ const moduleExports = {
 };
 ```
 
+Under the hood, the SDK is using a Webpack loader to wrap all your API route handlers and data fetching methods.
+
 ### Use `hidden-source-map`
 
 _(New in version 6.17.1, will default to `true` in 8.0.0 and beyond.)_