docs(docs): add O(n) Kadane implementation for Maximum Subarray solution

apps/docs/content/(05-decision-space)/greedy/53-maximum-subarray.mdx

@@ -40,4 +40,14 @@ If you have figured out the O(n) solution, try coding another solution using the
 ```py
 class Solution:
     def maxSubArray(self, nums: list[int]) -> int:
+        best, total = nums[0], nums[0]
+
+        for i in range(1, len(nums)):
+            if total < 0:
+                total = nums[i]
+            else:
+                total = total + nums[i]
+            best = max(best, total)
+
+        return best
 ```