parser: print help when no args

Also create utility script for testing

src/caelestia/__init__.py

@@ -2,12 +2,12 @@ from caelestia.parser import parse_args
 
 
 def main() -> None:
-    args = parse_args()
+    parser, args = parse_args()
     if "cls" in args:
         args.cls(args).run()
     else:
-        import sys
-        print("No arguments given", file=sys.stderr)
+        parser.print_help()
+
 
 if __name__ == "__main__":
     main()