Document that "-" is supported for stdin in logfile argument.

apachedex/__init__.py

@@ -933,7 +933,7 @@ def main():
   parser = argparse.ArgumentParser(description='Compute Apdex out of '
     'apache-style log files')
   parser.add_argument('logfile', nargs='*',
-    help='Log files to process')
+    help='Log files to process. Use - for stdin.')
   parser.add_argument('-l', '--logformat',
     default='%h %l %u %t "%r" %>s %O "%{Referer}i" "%{User-Agent}i" %D',
     help='Apache LogFormat used to generate provided logs. '