add snippet fibonacciTillNum

snippets/fibonacciTillNum.md

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+### fibonaciiTillNum
+
+Generates an array, containing the Fibonacci sequence, up until the nth term.
+
+Create an empty array of the specific length, initializing the first two values (`0` and `1`).
+Use `Array.reduce()` to add values into the array, using the sum of the last two values, except for the first two.
+Uses a mathematical formula to calculate the length of the array required
+```js
+const fibonacciTillNum = num => {
+  let n = Math.ceil(Math.log(num * Math.sqrt(5) + 1/2) / Math.log((Math.sqrt(5)+1)/2))// fibonacci(5) -> [0,1,1,2,3];
+  return Array.from({ length: n}).reduce((acc, val, i) => acc.concat(i > 1 ? acc[i - 1] + acc[i - 2] : i), []);
+  }
+  \\ fibsTillNum(15) -> [0,1,1,2,3,5,8,13]
+```