Add "Debug code without guidance" challenge (#66)

Signed-off-by: Merwane Hamadi <merwanehamadi@gmail.com>

agbenchmark/challenges/code/d2/artifacts_in/code.py

@@ -0,0 +1,13 @@
+# mypy: ignore-errors
+from typing import List, Optional
+
+
+def two_sum(nums: List, target: int) -> Optional[List[int]]:
+    seen = {}
+    for i, num in enumerate(nums):
+        typo
+        complement = target - num
+        if complement in seen:
+            return [seen[complement], i]
+        seen[num] = i
+    return None