LogAnalyzer: added help text for --format option

Tools/LogAnalyzer/LogAnalyzer.py

@@ -211,7 +211,7 @@ def main():
     # deal with command line arguments
     parser = argparse.ArgumentParser(description='Analyze an APM Dataflash log for known issues')
     parser.add_argument('logfile', type=argparse.FileType('r'), help='path to Dataflash log file (or - for stdin)')
-    parser.add_argument('-f', '--format',  metavar='', type=str, action='store', choices=['bin','log','auto'], default='auto')
+    parser.add_argument('-f', '--format',  metavar='', type=str, action='store', choices=['bin','log','auto'], default='auto', help='log file format: \'bin\',\'log\' or \'auto\'')
     parser.add_argument('-q', '--quiet',  metavar='', action='store_const', const=True, help='quiet mode, do not print results')
     parser.add_argument('-p', '--profile', metavar='', action='store_const', const=True, help='output performance profiling data')
     parser.add_argument('-s', '--skip_bad', metavar='', action='store_const', const=True, help='skip over corrupt dataflash lines')