Update README with LeetCode Daily Challenge

Author: jeremymanning

README.md

@@ -123,6 +123,7 @@ _**Note:** Our group is currently taking a break from grinding leetcode. The tab
 | October 18, 2024 | [2044](https://leetcode.com/problems/count-number-of-maximum-bitwise-or-subsets/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/2044) | 🟡 Medium |
 | October 19, 2024 | [1545](https://leetcode.com/problems/find-kth-bit-in-nth-binary-string/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/1545) | 🟡 Medium |
 | October 20, 2024 | [1106](https://leetcode.com/problems/parsing-a-boolean-expression/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/1106) | 🔴 Hard |
+| October 21, 2024 | [1593](https://leetcode.com/problems/split-a-string-into-the-max-number-of-unique-substrings/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/1593) | 🟡 Medium |
 
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