[options] Document that postprocessing is not forced by --postprocessor-args

Resolves #30307

youtube_dl/options.py

@@ -801,7 +801,7 @@ def parseOpts(overrideArguments=None):
     postproc.add_option(
         '--postprocessor-args',
         dest='postprocessor_args', metavar='ARGS',
-        help='Give these arguments to the postprocessor')
+        help='Give these arguments to the postprocessor (if postprocessing is required)')
     postproc.add_option(
         '-k', '--keep-video',
         action='store_true', dest='keepvideo', default=False,