Add usage documentation.

Evidently the test environment does not contain the python sh module as indicated by this tox failure:

__________ ERROR collecting molecule_lxd/test/functional/test_func.py __________
molecule_lxd/test/functional/test_func.py:24: in <module>

How do I go about fixing this?

The proposed prepare.yml playbook is not idempotent and causes tox pre-checkin failure. We should either not fix and request an exception or find a fix - set task to change never?

Quack,

I wondered if with the switch to v3 things changed but this is still needed:

Skipping, cleanup playbook not configured.
Skipping, destroy action has no playbook.

and they are not contained in either molecule or molecule-lxd.

\_o<

virtual machines don't have the security.nesting key.

hardcoded in https://github.com/ansible-community/molecule-lxd/blob/main/src/molecule_lxd/playbooks/create.yml#L16

currently this breaks type: virtual-machine in settings:
"Failed creating instance record: Unknown configuration key: security.nesting"