Add 168 python solution (qiyuangong#38)

* Add 168_Excel_Sheet_Column_Title.py, by @yuchenliu15

Author: yuchenliu15

python/168_Excel_Sheet_Column_Title.py

@@ -0,0 +1,8 @@
+class Solution:
+    def convertToTitle(self, n: int) -> str:
+        res = ""
+        while n > 0:
+            n -= 1
+            res = chr(65 + n % 26) + res
+            n //= 26
+        return res