Update README.md

Geekhyt · web-flow · commit bda6ddac2ac8 · 2021-02-02T01:52:48.000+08:00
diff --git a/README.md b/README.md
@@ -26,3 +26,4 @@
 - [144. 二叉树的前序遍历](https://github.com/Geekhyt/javascript-leetcode/issues/14)
 - [145. 二叉树的后序遍历](https://github.com/Geekhyt/javascript-leetcode/issues/15)
 - [100. 相同的树](https://github.com/Geekhyt/javascript-leetcode/issues/16)
+- [101. 对称二叉树](https://github.com/Geekhyt/javascript-leetcode/issues/17)
