Add description to the CLI.

check_mysql_slave/__init__.py

@@ -27,7 +27,7 @@ def getSlaveStatus(host, user, passwd, port):
 
 
 def main():
-    parser = ArgumentParser()
+    parser = ArgumentParser(description='Check MySQL seconds behind master for Nagios-like monitoring.')
     parser.add_argument('-u',
                         '--user',
                         help='Login username',