Update README.md

leetcode144：二叉树的前序遍历

Author: sisterAn

README.md

@@ -69,6 +69,9 @@
 - [字节&leetcode151：翻转字符串里的单词](https://github.com/sisterAn/JavaScript-Algorithms/issues/18)
 - [字节&Leetcode3：无重复字符的最长子串](https://github.com/sisterAn/JavaScript-Algorithms/issues/21)
 
+#### 树
+- [leetcode144：二叉树的前序遍历](https://github.com/sisterAn/JavaScript-Algorithms/issues/37)
+
 #### 编程题
 - [携程&蘑菇街&bilibili：手写数组去重、扁平化函数](https://github.com/sisterAn/JavaScript-Algorithms/issues/30)
 - [百度：模版渲染](https://github.com/sisterAn/JavaScript-Algorithms/issues/36)