Allow dead code to avoid warning

Author: Bi0T1N

src/flow_control/match/guard.md

@@ -3,6 +3,7 @@
 A `match` *guard* can be added to filter the arm.
 
 ```rust,editable
+#[allow(dead_code)]
 enum Temperature {
     Celsius(i32),
     Fahrenheit(i32),