make min max average and sum snippets

snippets/max.md

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+### max
+
+Returns the maximum value out of two or more numbers/arrays.
+
+Use `Math.max()` combined with the spread operator (`...`) to get the maximum value in the array.
+
+```js
+const max = (...arr) => Math.max(...[].concat(...arr);
+```
+
+```js
+max([10, 1, 5]); // 10
+```