update CHANGELOG.md

Author: KoyanagiHitoshi

CHANGELOG.md

@@ -1,5 +1,10 @@
 # Change Log
 
+## [v3.8.0](https://github.com/KoyanagiHitoshi/AtCoder-Python-Introduction/releases/tag/v3.8.0) / 2023-09-24
+
+* [#29](https://github.com/KoyanagiHitoshi/AtCoder-Python-Introduction/pull/29) add code
+* [#29](https://github.com/KoyanagiHitoshi/AtCoder-Python-Introduction/pull/29) update CHANGELOG.md
+
 ## [v3.7.0](https://github.com/KoyanagiHitoshi/AtCoder-Python-Introduction/releases/tag/v3.7.0) / 2023-09-17
 
 * [#28](https://github.com/KoyanagiHitoshi/AtCoder-Python-Introduction/pull/28) upgrade Python (3.8.2) => (CPython 3.11.4)