Add documentation on `cloud-init` and `qemu-guest-agent`

[zdzielinski]

Ran into this when first using this provider, it might be nice to document that installing various cloud-init packages and the qemu-guest-agent (as well as enabling their services) is required for using VM templates with initialization data and/or obtaining specific IP and associated data from VM's. Having this in the VM documentation section could have saved me an (albeit small) amount of time.

[zdzielinski]

Closed the initial pull request to move toward a specific branch instead of master on my upstream repository.

[janosdebugs]

Hello @zdzielinski, #281 should add the necessary data source for the IP address reporting. Since both the IP address reporting and the ovirt_vm resource have initialization-related components, the best way to document this would be a guide as described in the Terraform plugin docs. Would you be up for writing such a guide for the new Terraform provider?