Added documentation

Change-Id: I4cb4c8c56642337899d0865c147b54df72b2c1fa
diff --git a/roles/kubernetes/defaults/main.yml b/roles/kubernetes/defaults/main.yml
index 74f6c2c..7e0d154 100644
--- a/roles/kubernetes/defaults/main.yml
+++ b/roles/kubernetes/defaults/main.yml
@@ -1,23 +1,38 @@
-# Copyright (c) 2022 VEXXHOST, Inc.
-#
-# Licensed under the Apache License, Version 2.0 (the "License"); you may
-# not use this file except in compliance with the License. You may obtain
-# a copy of the License at
-#
-#      http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
-# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
-# License for the specific language governing permissions and limitations
-# under the License.
+---
+# .. vim: foldmarker=[[[,]]]:foldmethod=marker
 
+# .. Copyright (C) 2022 VEXXHOST, Inc.
+# .. SPDX-License-Identifier: Apache-2.0
+
+# Default variables
+# =================
+
+# .. contents:: Sections
+#    :local:
+
+
+# .. envvar:: kubernetes_repo_url [[[
+#
+# Kubernetes repository URL
 kubernetes_repo_url: "{{ _kubernetes_upstream_apt_repository }}"
+
+                                                                   # ]]]
+# .. envvar:: kubernetes_version [[[
+#
+# Kubernetes version
 kubernetes_version: 1.22.7
 
+                                                                   # ]]]
+# .. envvar:: kubernetes_kernel_modules [[[
+#
+# List of kernel modules to be automatically loaded
 kubernetes_kernel_modules:
   - br_netfilter
 
+                                                                   # ]]]
+# .. envvar:: kubernetes_sysctls [[[
+#
+# List of ``sysctl`` parameters to set
 kubernetes_sysctls:
   - name: net.ipv4.ip_forward
     value: 1
@@ -32,4 +47,10 @@
   - name: net.ipv4.conf.all.rp_filter
     value: 0
 
+                                                                   # ]]]
+# .. envvar:: kubernetes_control_plane_group [[[
+#
+# Name of Ansible group containing all control-plane nodes
 kubernetes_control_plane_group: controllers
+
+                                                                   # ]]]