add mutation example

Author: Adrinlol

README.md

@@ -486,3 +486,33 @@ function getIndexToIns(arr, num) {
 
 getIndexToIns([10, 20, 30, 40, 50], 35);
 ```
+
+### 15. Mutations
+
+_Difficulty: Beginner_
+
+Return `true` if the string in the first element of the array contains all of the letters of the string in the second element of the array.
+
+For example, ["hello", "Hello"], should return `true` because all of the letters in the second string are present in the first, ignoring case.
+
+The arguments `["hello", "hey"]` should return `false` because the string `hello` does not contain a `y`.
+
+Lastly, `["Alien", "line"]`, should return `true` because all of the letters in `line` are present in `Alien`.
+
+---
+
+#### Solution
+
+```js
+function mutation(arr) {
+  const arr1 = arr[0].toLowerCase().split("");
+  const arr2 = arr[1].toLowerCase().split("");
+  for (let i = 0; i < arr2.length; i++) {
+    if (arr1.indexOf(arr2[i]) == -1) {
+      return false;
+    }
+  }
+  return true;
+}
+mutation(["hello", "hey"]);
+```