Fix missing call to self.queue.submit

docs/beginner/tutorial2-swapchain/README.md

@@ -257,6 +257,7 @@ Now we can actually get to clearing the screen (long time coming). We need to us
         });
     }
     
+    self.queue.submit([
         encoder.finish()
     ]);
 }
@@ -337,4 +338,4 @@ In the event loop we're currently using `*control_flow = ControlFlow::Wait` in m
 
 Modify the `input()` method to capture mouse events, and update the clear color using that. *Hint: you'll probably need to use `WindowEvent::CursorMoved`*
 
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