Add gpiod.c for libgpiod output sample code

guowenxue

2021-01-23 7baed996272cd3c889a5ab714c2b3391703f75f1

 apue/2.Socket/ds18b20.c

@@ -98,5 +98,7 @@
    /* convert string value to float value */
    *temp = atof(ptr)/1000;
   
    close(fd);

    return 0;
}