Fixed playbooks path in Vagrant and Readme (#341)

Start provisioning of the cluster using the following command:

```bash

ansible-playbook playbook/site.yml -i inventory.yml

ansible-playbook playbooks/site.yml -i inventory.yml

```

## Upgrading

A playbook is provided to upgrade K3s on all nodes in the cluster. To use it, update `k3s_version` with the desired version in `inventory.yml` and run:

```bash

ansible-playbook playbook/upgrade.yml -i inventory.yml

ansible-playbook playbooks/upgrade.yml -i inventory.yml

```

## Airgap Install

An example folder for an x86_64 cluster:

```bash

$ ls ./playbook/my-airgap/

$ ls ./playbooks/my-airgap/

total 248M

-rwxr-xr-x 1 $USER $USER  58M Nov 14 11:28 k3s

-rw-r--r-- 1 $USER $USER 190M Nov 14 11:30 k3s-airgap-images-amd64.tar.gz

$ cat inventory.yml

...

airgap_dir: ./my-airgap # Paths are relative to the playbook directory

airgap_dir: ./my-airgap # Paths are relative to the playbooks directory

```

Additionally, if deploying on a OS with SELinux, you will also need to download the latest [k3s-selinux RPM](https://github.com/k3s-io/k3s-selinux/releases/latest) and place it in the airgap folder.

  vm.provision "ansible", run: 'once' do |ansible|

    ansible.compatibility_mode = "2.0"

    ansible.playbook = "playbook/site.yml"

    ansible.playbook = "playbooks/site.yml"

    ansible.groups = {

      "server" => NODE_ROLES.grep(/^server/),

      "agent" => NODE_ROLES.grep(/^agent/),