Update README.md

Author: hiro032

README.md

@@ -3,6 +3,22 @@
 [VS Code로 보기](https://github1s.com/ksundong/backend-interview-question)
 
 + html내 마크다운 문법 사용법
+예시)
+<details><summary style="color:skyblue">CLICK ME</summary>
+<p>
+
+#### yes, even hidden code blocks!
+## hi
+** 강조 **
+- 1
+- 2
+- 3
+```python
+print("hello world!")
+```
+
+</p>
+</details>
 
 ## Table Of Contents