Fix code example – add StyledButton (#323)

... so that LogoutButton works fine

docs/source/tutorial/local-state.md

@@ -249,6 +249,12 @@ export default function LogoutButton() {
     </ApolloConsumer>
   );
 }
+
+const StyledButton = styled("button")(menuItemClassName, {
+  background: "none",
+  border: "none",
+  padding: 0
+});
 ```
 
 When we click the button, we perform a direct cache write by calling `client.writeData` and passing in a data object that sets the `isLoggedIn` boolean to false.