Update README with LeetCode Daily Challenge

Author: jeremymanning

README.md

@@ -390,6 +390,7 @@ _**Note:** Our group is currently taking a break from grinding leetcode. The tab
 | July 12, 2025 | [1900](https://leetcode.com/problems/the-earliest-and-latest-rounds-where-players-compete/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/1900) | 🔴 Hard |
 | July 13, 2025 | [2410](https://leetcode.com/problems/maximum-matching-of-players-with-trainers/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/2410) | 🟡 Medium |
 | July 14, 2025 | [1290](https://leetcode.com/problems/convert-binary-number-in-a-linked-list-to-integer/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/1290) | 🟢 Easy |
+| July 15, 2025 | [3136](https://leetcode.com/problems/valid-word/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/3136) | 🟢 Easy |
 
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