Update README.md

Geekhyt · web-flow · commit 86c28bc20443 · 2021-02-22T12:48:13.000+08:00
diff --git a/README.md b/README.md
@@ -52,3 +52,6 @@
 - [40. 组合总和 II](https://github.com/Geekhyt/javascript-leetcode/issues/31)
 - [77. 组合](https://github.com/Geekhyt/javascript-leetcode/issues/33)
 - [78. 子集](https://github.com/Geekhyt/javascript-leetcode/issues/34)
+
+## 字符串
+- [125. 验证回文串](https://github.com/Geekhyt/javascript-leetcode/issues/35)
