create javascript/shuffle instructions

javascript/shuffle/README.md

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+*How to shuffle the characters in a string in JavaScript ?*
+
+e.g. Given "ABCDEFG", return something like "GEFBDCA".
+
+```js
+console.log(shuffle("the quick brown fox jumps over the lazy dog"));
+//-> "veolrm  hth  ke opynug tusbxq ocrad ofeizwj"
+
+console.log(shuffle("the quick brown fox jumps over the lazy dog"));
+//-> "o dt hutpe u iqrxj  yaenbwoolhsvmkcger ozf "
+```
+
+- Best performance case: O(n)
+- Worst performance case: O(n log n)