Update README with LeetCode Daily Challenge

Author: jeremymanning

README.md

@@ -28,6 +28,7 @@ Each day (ideally) we'll attempt the daily [leetcode](https://leetcode.com) prob
 | July 17, 2024 | [1110](https://leetcode.com/problems/delete-nodes-and-return-forest/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/1110) | 🟡 Medium |
 | July 18, 2024 | [1530](https://leetcode.com/problems/number-of-good-leaf-nodes-pairs/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/1530) | 🟡 Medium |
 | July 19, 2024 | [1380](https://leetcode.com/problems/lucky-numbers-in-a-matrix/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/1380) | 🟢 Easy |
+| July 20, 2024 | [1605](https://leetcode.com/problems/find-valid-matrix-given-row-and-column-sums/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/1605) | 🟡 Medium |
 
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