Update kubeadm_join_phases_skip comment

Co-authored-by: Cristian Calin <6627509+cristicalin@users.noreply.github.com>

roles/kubespray-defaults/defaults/main.yaml

@@ -38,7 +38,8 @@ kubeadm_init_phases_skip: >-
   {{ kubeadm_init_phases_skip_default }}
   {%- endif -%}
 
-## List of kubeadm join phases that should be skipped when joining to the control plane
+# List of kubeadm phases that should be skipped when joining a new node
+# You may need to set this to ['preflight'] for air-gaped deployments to avoid failing connectivity tests.
 kubeadm_join_phases_skip: []
 
 # A string slice of values which specify the addresses to use for NodePorts.