Update README with LeetCode Daily Challenge

Author: jeremymanning

README.md

@@ -191,6 +191,7 @@ _**Note:** Our group is currently taking a break from grinding leetcode. The tab
 | December 25, 2024 | [515](https://leetcode.com/problems/find-largest-value-in-each-tree-row/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/515) | 🟡 Medium |
 | December 26, 2024 | [494](https://leetcode.com/problems/target-sum/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/494) | 🟡 Medium |
 | December 27, 2024 | [1014](https://leetcode.com/problems/best-sightseeing-pair/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/1014) | 🟡 Medium |
+| December 28, 2024 | [689](https://leetcode.com/problems/maximum-sum-of-3-non-overlapping-subarrays/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/689) | 🔴 Hard |
 
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