Added samples

snippets/flatten-array.md

@@ -6,4 +6,5 @@ Use `reduce()` to get all elements that are not arrays, flatten each element tha
 ```js
 const flatten = arr =>
   arr.reduce( (a, v) => a.concat( Array.isArray(v) ? flatten(v) : v ), []);
+// flatten([1,[2],[[3],4],5]) -> [1,2,3,4,5]
 ```