更新readme

README.md

@@ -55,6 +55,7 @@ leetcode 题解，记录自己的 leecode 解题之路。
 - [201.bitwise-and-of-numbers-range](./problems/201.bitwise-and-of-numbers-range.md)
 - [209.minimum-size-subarray-sum](./problems/209.minimum-size-subarray-sum.md)
 - [900.rle-iterator](./problems/900.rle-iterator.md)
+- [322.coin-change](./problems/322.coin-change.md)
 
 #### 困难难度