docs: added ref to backups
diff --git a/roles/percona_xtradb_cluster/defaults/main.yml b/roles/percona_xtradb_cluster/defaults/main.yml
index 53583c4..c8542e8 100644
--- a/roles/percona_xtradb_cluster/defaults/main.yml
+++ b/roles/percona_xtradb_cluster/defaults/main.yml
@@ -1,4 +1,6 @@
# This variable allows you to add configuration options to `spec` field on the
# PerconaXtraDBCluster object in Kubernetes. It can be used to enable features
# such as backups.
+#
+# See: https://docs.percona.com/percona-operator-for-mysql/pxc/backups.html
percona_xtradb_cluster_spec: {}