Added README.md for roles

Signed-off-by: Tuan-Dat Tran <tuan-dat.tran@tudattr.dev>

roles/k3s_agent/README.md

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+# K3s Agent Ansible Role
+
+This Ansible role installs and configures a K3s agent on a node.
+
+## Role Variables
+
+- `k3s.loadbalancer.default_port`: The port for the K3s load balancer. Defaults to `6443`.
+- `k3s_token`: The token for joining the K3s cluster. This is a required variable.
+- `hostvars['k3s-loadbalancer'].ansible_default_ipv4.address`: The IP address of the K3s load balancer. This is a required variable.
+
+## Tasks
+
+The main tasks are in `tasks/main.yml` and `tasks/installation.yml`.
+
+- **`installation.yml`**:
+  - Installs `qemu-guest-agent`.
+  - Checks if K3s is already installed.
+  - Downloads the K3s installation script to `/tmp/k3s_install.sh`.
+  - Installs K3s as an agent, connecting to the master.
+
+## Handlers
+
+The main handlers are in `handlers/main.yml`.
+
+- **`Restart k3s`**: Restarts the `k3s` service.
+
+## Usage
+
+Here is an example of how to use this role in a playbook:
+
+```yaml
+---
+- hosts: k3s_agents
+  roles:
+    - role: k3s_agent
+      vars:
+        k3s_token: "your_k3s_token"
+        k3s.loadbalancer.default_port: 6443
+```