Update CONTRIBUTING.md

Change-Id: I2e652675d6f39ce23b0f9946236584ec96683f2c

Author: winstonsung

CONTRIBUTING.md

@@ -116,6 +116,12 @@ python_module.py
 ```
 
 ```py
+"""
+Summary of module.
+
+Extended description.
+"""
+
 # Standard imports
 import standard_import