[Password manager Python tests] Add a comment on logging

components/test/data/password_manager/automated_tests/run_tests.py

 # -*- coding: utf-8 -*-
 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Encapsulates running tests defined in tests.py.
 
 Running this script requires passing --config-path with a path to a config file
 of the following structure:
 
   [data_files]
   passwords_path=<path to a file with passwords>
   [binaries]
   chrome-path=<chrome binary path>
   chromedriver-path=<chrome driver path>
   [run_options]
   # |tests_in_parallel| is optional, the default value is 1.
   tests_in_parallel=<number of parallel tests>
   # |tests_to_runs| field is optional, if it is absent all tests will be run.
   tests_to_run=<test names to run, comma delimited>
+
+The script uses the Python's logging library to report the test results,
+as well as debugging information. It emits three levels of logs (in
+descending order of severity):
+  logging.INFO: Summary of the tests.
+  logging.DEBUG: Details about tests failures.
+  SCRIPT_DEBUG (see below): Debug info of this script.
+You have to set up appropriate logging handlers to have the logs appear.
 """
 import argparse
 import ConfigParser
 import logging
 import os
 import shutil
 import subprocess
 import tempfile
 import time
 
@@ skipping 188 matching lines @@
 def main():
   parser = argparse.ArgumentParser()
   parser.add_argument("config_path", metavar="N",
                       help="Path to the config.ini file.")
   args = parser.parse_args()
   run_tests(args.config_path)
 
 
 if __name__ == "__main__":
   main()