update readme.md

Author: DaleSeo

README.md

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 [![Automation 🤖](https://github.com/DaleStudy/leetcode-study/actions/workflows/automation.yaml/badge.svg)](https://github.com/DaleStudy/leetcode-study/actions/workflows/automation.yaml)
 [![Integration 🔄](https://github.com/DaleStudy/leetcode-study/actions/workflows/integration.yaml/badge.svg)](https://github.com/DaleStudy/leetcode-study/actions/workflows/integration.yaml)
 
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 🛫 해외취업을 위한 오픈소스 기반 알고리즘 스터디
 
 - [웹사이트](https://www.dalestudy.com/)
-- [리더보드 (개발 중)](https://leaderboard.dalestudy.com/)
+- [리더보드](https://leaderboard.dalestudy.com/)
 - [위키](https://github.com/DaleStudy/leetcode-study/wiki)
 - [게시판](https://github.com/DaleStudy/leetcode-study/discussions)
 - [채팅방](https://discord.com/channels/775115965964222492/1229860988170403901)
 
 ## 차수
 
+- 4기 (Mar 30, 2025 - Jul 12, 2025): [프로젝트](https://github.com/orgs/DaleStudy/projects/13/views/3), [팀](https://github.com/orgs/DaleStudy/teams/leetcode04)
 - 3기 (Dec 08, 2024 - Mar 22, 2025): [프로젝트](https://github.com/orgs/DaleStudy/projects/12/views/3), [팀](https://github.com/orgs/DaleStudy/teams/leetcode03)
 - 2기 (Aug 11, 2024 - Nov 23, 2024): [프로젝트](https://github.com/orgs/DaleStudy/projects/3/views/3), [팀](https://github.com/orgs/DaleStudy/teams/leetcode02)
 - 1기 (Apr 21, 2024 - Aug 10, 2024): [프로젝트](https://github.com/orgs/DaleStudy/projects/1/views/1), [팀](https://github.com/orgs/DaleStudy/teams/leetcode01)
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