Persistence.txt enhancements

[nikmartin]

It would be helpful for users if Persistence.txt showed how to gather the information required for the udev rules:

1) Change <cache_match_expr> to ENV{ID_SERIAL}=="<ID SERIAL OF YOUR CACHE DEVICE>", ENV{DEVTYPE}==<DEVICE TYPE OF YOUR CACHE DEVICE>

2) Change <source_match_expr> to ENV{ID_SERIAL}=="<ID SERIAL OF YOUR HARD DISK>", ENV{DEVTYPE}==<DEVICE TYPE OF YOUR SOURCE DEVICE>

Find <ID SERIAL OF YOUR xxx DEVICE> and <DEVICE TYPE OF YOUR xxx DEVICE> by running:
    udevadm info --query=env --name=/dev/<source disk or partition name>
and in the output, find the items:
ID_SERIAL
and
DEVTYPE
respectively.

[sanoj-stec]

I will add a script for this soon
The script will add udev rules during cache creation and remove it on cache deletion

[sanoj-stec]

added the script for rule file generation in commit e17e850