Added snippet to sample an array

snippets/array-sample.md

@@ -0,0 +1,9 @@
+### Array sample
+
+Use `Math.random()` to generate a random number, multiply it with `Array.length` and round it of to the nearest whole number using `Math.floor()`. Works with strings too. 
+
+```js
+const sample = arr => arr[Math.floor(Math.random() * arr.length)];
+
+// sample([3, 7, 9, 11]) -> 9 
+```