parse-options: clarify what "negated" means for PARSE_OPT_NONEG

The documentation says the flag prevents an option from being
"negated" without specifying what that means. Add a parenthetical
to clarify that it rejects the "--no-<option>" form.

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: mmontalbo

parse-options.h

@@ -117,6 +117,7 @@ typedef int parse_opt_subcommand_fn(int argc, const char **argv,
  *   PARSE_OPT_OPTARG: says that the argument is optional (not for BOOLEANs)
  *   PARSE_OPT_NOARG: says that this option does not take an argument
  *   PARSE_OPT_NONEG: says that this option cannot be negated
+ *                   (i.e. rejects "--no-<option>")
  *   PARSE_OPT_HIDDEN: this option is skipped in the default usage, and
  *                     shown only in the full usage.
  *   PARSE_OPT_LASTARG_DEFAULT: says that this option will take the default