Add comment on unchecked arithmetic (division by zero) in Math.sol (#4050)

Co-authored-by: Francisco <fg@frang.io>

contracts/utils/math/Math.sol

@@ -67,6 +67,9 @@ library Math {
 
             // Handle non-overflow cases, 256 by 256 division.
             if (prod1 == 0) {
+                // Solidity will revert if denominator == 0, unlike the div opcode on its own.
+                // The surrounding unchecked block does not change this fact.
+                // See https://docs.soliditylang.org/en/latest/control-structures.html#checked-or-unchecked-arithmetic.
                 return prod0 / denominator;
             }