Document the terraform option master_allowed_ports (#7196)

Implemented in #6547

contrib/terraform/openstack/README.md

@@ -269,6 +269,7 @@ For your cluster, edit `inventory/$CLUSTER/cluster.tfvars`.
 |`master_allowed_remote_ips` | List of CIDR blocks allowed to initiate an API connection, `["0.0.0.0/0"]` by default |
 |`k8s_allowed_remote_ips` | List of CIDR allowed to initiate a SSH connection, empty by default |
 |`worker_allowed_ports` | List of ports to open on worker nodes, `[{ "protocol" = "tcp", "port_range_min" = 30000, "port_range_max" = 32767, "remote_ip_prefix" = "0.0.0.0/0"}]` by default |
+|`master_allowed_ports` | List of ports to open on master nodes, expected format is `[{ "protocol" = "tcp", "port_range_min" = 443, "port_range_max" = 443, "remote_ip_prefix" = "0.0.0.0/0"}]`, empty by default |
 |`wait_for_floatingip` | Let Terraform poll the instance until the floating IP has been associated, `false` by default. |
 |`node_root_volume_size_in_gb` | Size of the root volume for nodes, 0 to use ephemeral storage |
 |`master_root_volume_size_in_gb` | Size of the root volume for masters, 0 to use ephemeral storage |