Update README with LeetCode Daily Challenge

Author: jeremymanning

README.md

@@ -86,6 +86,7 @@ Each day (ideally) we'll attempt the daily [leetcode](https://leetcode.com) prob
 | September 13, 2024 | [1310](https://leetcode.com/problems/xor-queries-of-a-subarray/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/1310) | 🟡 Medium |
 | September 14, 2024 | [2419](https://leetcode.com/problems/longest-subarray-with-maximum-bitwise-and/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/2419) | 🟡 Medium |
 | September 15, 2024 | [1371](https://leetcode.com/problems/find-the-longest-substring-containing-vowels-in-even-counts/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/1371) | 🟡 Medium |
+| September 16, 2024 | [539](https://leetcode.com/problems/minimum-time-difference/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/539) | 🟡 Medium |
 
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