log: Improve the documentation for tor_log_update_sigsafe_err_fds()

  n_fds = 1;

  for (lf = logfiles; lf; lf = lf->next) {

     /* Don't try callback to the control port, or syslogs: We can't

      * do them from a signal handler. Don't try stdout: we always do stderr.

     /* Don't try callback to the control port, syslogs, android logs, or any

      * other non-file descriptor log: We can't call arbitrary functions from a

      * signal handler.

      */

    if (lf->is_temporary || logfile_is_external(lf)

        || lf->seems_dead || lf->fd < 0)

  if (!found_real_stderr &&

      int_array_contains(log_fds, n_fds, STDOUT_FILENO)) {

    /* Don't use a virtual stderr when we're also logging to stdout. */

    /* Don't use a virtual stderr when we're also logging to stdout.

     * If we reached max_fds logs, we'll now have (max_fds - 1) logs.

     * That's ok, max_fds is large enough that most tor instances don't exceed

     * it. */

    raw_assert(n_fds >= 2); /* Don't tor_assert inside log fns */

    --n_fds;

    log_fds[0] = log_fds[n_fds];