Add readme

Author: Khanh Do

README.md

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+# LeetCode Python Solutions
+This repo contains my Python solutions to LeetCode problems. I try to give ample
+documentation to maximize the pedagogy of my solutions, including time and space
+complexity and how I arrived at them.
+
+For expediency, when problems involve an array, I am OK with using a Python list
+instead and using the following operations:
+- `for i in range(n)` to iterate over the list
+-  `for i in range(bigger, smaller, -1)` to iterate backwards
+- `nums[-1]` to get the last element
+
+While these operations are indeed Pythonic, they don't provide any extra
+functionality as compared to a low-level array. No short-cuts are intended.
+
+I very much welcome corrections. Thanks.