Added missing os and sys for python domain

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cc: @PatrickFarley

Author: ram-msft

articles/cognitive-services/Computer-vision/QuickStarts/python-domain.md

@@ -39,6 +39,8 @@ To create and run the landmark sample, do the following steps:
 1. At the prompt, use the `python` command to run the sample. For example, `python get-landmarks.py`.
 
 ```python
+import os
+import sys
 import requests
 # If you are using a Jupyter notebook, uncomment the following line.
 # %matplotlib inline