Move all notes and warnings to description text.
Refine some small clarification.
Do not use NOTE/WARNING unless there is a serious reason (data loss).
We can not link internal VK kernel key in custom user
keyring. There are two reasons for it:
The internal VK kernel key description can not be
acquired via API and it may change over time
(LUKS2 reencryption).
With recent SED OPAL support volume key becomes a 'blob'
containing up to two keys (dm-crypt key for SWE and key
for unlocking SED OPAL locking range). The internal
kernel key contains only dm-crypt (if required) but
custom user keyring needs to be provided with whole
volume key (blob).
Added user specified key description for the linked key
in custom user keyring. The linked key can be reached by
the specified description after successful activation (resume).
Add --volume-key-keyring option, which takes a name of a key in keyring,
which will be used as a VK during device activation. The key can be
specified in keyctl-compatible syntax "%<key_type>:<key_name>".
