Added samples

snippets/average-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 average = arr =>
   arr.reduce( (acc , val) => acc + val, 0) / arr.length;
+// average([1,2,3]) -> 2
 ```