Update and rename concat.md to array-concatenation.md

snippets/array-concatenation.md

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+### Array concatenation
+
+Use `Array.concat()` to concatenate and array with any additional arrays and/or values, specified in `args`.
+
+```js
+const ArrayConcat = (arr, ...args) => arr.concat(...args); 
+// ArrayConcat([1], [1, 2, 3, [4]]) -> [1, 2, 3, [4]]
+```