add youtube link for 21

fishercoder1534 · fishercoder1534 · commit a42122059fa7 · 2020-02-11T08:30:51.000-08:00
diff --git a/README.md b/README.md
@@ -850,7 +850,7 @@ _If you like this project, please leave me a star._ &#9733;
 |24|[Swap Nodes in Pairs](https://leetcode.com/problems/swap-nodes-in-pairs/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_24.java)||Medium| Recursion, LinkedList
 |23|[Merge k Sorted Lists](https://leetcode.com/problems/merge-k-sorted-lists/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_23.java)|[:tv:](https://www.youtube.com/watch?v=Llse1tImXQA)|Hard|Heap
 |22|[Generate Parentheses](https://leetcode.com/problems/generate-parentheses/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_22.java)||Medium|Backtracking
-|21|[Merge Two Sorted Lists](https://leetcode.com/problems/merge-two-sorted-lists/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_21.java)||Easy| Recursion
+|21|[Merge Two Sorted Lists](https://leetcode.com/problems/merge-two-sorted-lists/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_21.java)|[:tv:](https://youtu.be/N8WTaSSivEI)|Easy| Recursion
 |20|[Valid Parentheses](https://leetcode.com/problems/valid-parentheses/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_20.java)|[:tv:](https://www.youtube.com/watch?v=eBbg5pnq5Zg)|Easy|Stack
 |19|[Remove Nth Node From End of List](https://leetcode.com/problems/remove-nth-node-from-end-of-list/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_19.java)|[:tv:](https://youtu.be/Kka8VgyFZfc)|Medium| Linked List
 |18|[4 Sum](https://leetcode.com/problems/4sum/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_18.java)||Medium|Two Pointers
