Modify help msg if invalid input

Author: bjk7119

README.md

@@ -62,11 +62,11 @@ fosslight [Mode] [option1] <arg1> [option2] <arg2>...
 ### Parameters   
 Mode
 ``` 
+        all                     Run all scanners(Default)
         source                  Run FOSSLight Source
         dependency              Run FOSSLight Dependency
         binary                  Run FOSSLight Binary
         prechecker              Run FOSSLight Prechecker
-        all                     Run all scanners
         compare                 Compare two FOSSLight reports
 ``` 
 Options:

src/fosslight_scanner/_help.py

@@ -13,6 +13,7 @@
 
     Parameters:
         Mode
+            all\t\t\t    Run all scanners(Default)
             source\t\t    Run FOSSLight Source
             dependency\t\t    Run FOSSLight Dependency
             binary\t\t    Run FOSSLight Binary

src/fosslight_scanner/cli.py

@@ -2,6 +2,7 @@
 # -*- coding: utf-8 -*-
 # Copyright (c) 2022 LG Electronics Inc.
 # SPDX-License-Identifier: Apache-2.0
+import sys
 from argparse import ArgumentParser
 from ._help import print_help_msg
 from .fosslight_scanner import run_main, PKG_NAME
@@ -28,7 +29,7 @@ def main():
     try:
         args = parser.parse_args()
     except SystemExit:
-        print_help_msg()
+        sys.exit(0)
 
     if args.help:
         print_help_msg()