Better documentation about environment variables

[process0]

Took a minute to figure out i needed to specify HCLOUD_NETWORK in the Deployment environment variables. Are these variables socumented somewhere that I missed? Also would it make more sense to store all of them in a Secret along with the token?

const (
	hcloudTokenENVVar                        = "HCLOUD_TOKEN"
	hcloudEndpointENVVar                     = "HCLOUD_ENDPOINT"
	hcloudNetworkENVVar                      = "HCLOUD_NETWORK"
	hcloudDebugENVVar                        = "HCLOUD_DEBUG"
	hcloudLoadBalancersEnabledENVVar         = "HCLOUD_LOAD_BALANCERS_ENABLED"
	hcloudLoadBalancersLocation              = "HCLOUD_LOAD_BALANCERS_LOCATION"
	hcloudLoadBalancersNetworkZone           = "HCLOUD_LOAD_BALANCERS_NETWORK_ZONE"
	hcloudLoadBalancersDisablePrivateIngress = "HCLOUD_LOAD_BALANCERS_DISABLE_PRIVATE_INGRESS"
	hcloudLoadBalancersUsePrivateIP          = "HCLOUD_LOAD_BALANCERS_USE_PRIVATE_IP"
	nodeNameENVVar                           = "NODE_NAME"
	providerName                             = "hcloud"
	providerVersion                          = "v1.9.1"
)