debug_guide for python SDK (Azure#19716)

Author: msyyc

doc/dev/debug_guide.md

@@ -0,0 +1,23 @@
+# Debug
+
+This guide is to help Python SDK users to get the process about how SDK call REST api
+
+(1) Copy the following code in your .py file
+```
+import sys
+import logging
+
+logger = logging.getLogger('')
+logger.setLevel(logging.DEBUG)
+handler = logging.StreamHandler(stream=sys.stdout, )
+logger.addHandler(handler)
+formatter = logging.Formatter(
+    '%(asctime)s - %(name)s - %(levelname)s - %(message)s')
+handler.setFormatter(formatter)
+```
+
+![Position example](./debug_guide_position.png "Position example")
+
+(2) Run your .py program and you could find the log info in screen. It is convenient to get the process about how SDK call REST api:
+
+![example](./debug_guide_example.png "example")