Move comment

docs/beginner/tutorial2-swapchain/README.md

@@ -4,9 +4,9 @@
 For convenience we're going to pack all the fields into a struct, and create some methods on that.
 
 ```rust
+// main.rs
 use winit::Window;
 
-// main.rs
 struct State {
     surface: wgpu::Surface,
     device: wgpu::Device,