Improve README for master/slave setup with hostname explanation

readme-vars.yml

@@ -12,6 +12,9 @@ available_architectures:
   - {arch: "{{ arch_arm64 }}", tag: "arm64v8-latest"}
 # container parameters
 param_container_name: "{{ project_name }}"
+param_usage_include_hostname: "optional"
+param_hostname: "hostname"
+param_hostname_desc: "In a master-slave architecture, the hostname of the master node is displayed as its name in the web interface, while the hostname of the slave nodes represents their device aliases. These slave hostnames must match the aliases defined in the master's Slaves file."
 param_usage_include_vols: true
 param_volumes:
   - {vol_path: "/config", vol_host_path: "/path/to/{{ project_name }}/config", desc: "Persistent config files"}