docs: add comments

backend/server.js

@@ -20,10 +20,13 @@ app.use(cors());
 app.use(express.json());
 app.use(express.urlencoded({ extended: false }));
 
+// Register routes
 app.use("/", indexRouter);
 app.use("/users", usersRouter);
-app.use(routeNotFoundJsonHandler);
-app.use(jsonErrorHandler);
+
+// Register 404 middleware and error handler
+app.use(routeNotFoundJsonHandler); // this middleware must be registered after all routes to handle 404 correctly
+app.use(jsonErrorHandler); // this error handler must be registered after all middlewares to catch all errors
 
 const port = parseInt(process.env.PORT || "3000");