Added samples

snippets/sum-of-array-of-numbers.md

@@ -5,4 +5,5 @@ Use `reduce()` to add each value to an accumulator, initialized with a value of
 ```js
 const sum = arr =>
   arr.reduce( (acc , val) => acc + val, 0);
+// sum([1,2,3,4]) -> 10
 ```