feat(README.md): add badge

Author: ryoppippi

README.md

@@ -1,7 +1,11 @@
 # ryoppippi's leetcode solutions
 
+[![LeetCode user ryoppippi](https://img.shields.io/badge/dynamic/json?style=for-the-badge&labelColor=black&color=%23ffa116&label=Solved&query=solved&url=https%3A%2F%2Fleetcode-badge.vercel.app%2Fapi%2Fusers%2Fryoppippi&logo=leetcode&logoColor=yellow)](https://leetcode.com/ryoppippi/)
+
 ## TODO
+
 - [ ] Add `flake.nix` currently I use `nix run github:clearloop/leetcode-cli`)
 
 ## LICENSE
+
 MIT