Add monitor diskmon

Output:

v@lenovoLaptop:~/Downloads$ ./diskmon.sh 
# HELP diskmon_is_rotational Information about disk being rotational.
# TYPE diskmon_is_rotational gauge
diskmon_is_rotational{device="sda1",fstype="vfat",mountpoint="/boot/efi"} 0
diskmon_is_rotational{device="sda5",fstype="ext4",mountpoint="/"} 0