📖 Update quick start about OpenStack

Author: hidekazuna

docs/book/src/user/quick-start.md

@@ -412,6 +412,27 @@ wget https://raw.githubusercontent.com/kubernetes-sigs/cluster-api-provider-open
 source /tmp/env.rc <path/to/clouds.yaml> <cloud>
 ```
 
+Apart from the script, the following OpenStack environment variables are required.
+```bash
+# The IP address on which the API server is serving.
+export OPENSTACK_CONTROLPLANE_IP=<control plane ip>
+# The ID of an external OpenStack Network. This is necessary to get public internet to the VMs.
+export OPENSTACK_EXTERNAL_NETWORK_ID=<external network id>
+# The list of nameservers for OpenStack Subnet being created.
+# Set this value when you need create a new network/subnet while the access through DNS is required.
+export OPENSTACK_DNS_NAMESERVERS=<dns nameserver>
+# FailureDomain is the failure domain the machine will be created in.
+export OPENSTACK_FAILURE_DOMAIN=<availability zone name>
+# The flavor reference for the flavor for your server instance.
+export OPENSTACK_CONTROL_PLANE_MACHINE_FLAVOR=<flavor>
+# The flavor reference for the flavor for your server instance.
+export OPENSTACK_NODE_MACHINE_FLAVOR=<flavor>
+# The name of the image to use for your server instance. If the RootVolume is specified, this will be ignored and use rootVolume directly.
+export OPENSTACK_IMAGE_NAME=<image name>
+# SSHAuthorizedKeys specifies a list of ssh authorized keys for the user
+export OPENSTACK_SSH_AUTHORIZED_KEY=<ssh key>
+```
+
 A full configuration reference can be found in [configuration.md](https://github.com/kubernetes-sigs/cluster-api-provider-openstack/blob/master/docs/configuration.md).
 
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