Fixed typo: BackendBit::Primary is from a previous version

docs/beginner/tutorial2-surface/README.md

@@ -51,7 +51,7 @@ impl State {
         let size = window.inner_size();
 
         // The instance is a handle to our GPU
-        // BackendBit::PRIMARY => Vulkan + Metal + DX12 + Browser WebGPU
+        // Backends::all => Vulkan + Metal + DX12 + Browser WebGPU
         let instance = wgpu::Instance::new(wgpu::Backends::all());
         let surface = unsafe { instance.create_surface(window) };
         let adapter = instance.request_adapter(