message: Add subnet_cidr_block configuration steps to README
diff: @@ -29,6 +29,14 @@ can be composed into a higher-level, reusable abstraction.
  $ pulumi config set gcp:region us-central1
  ```
  +1. Configure one or more subnetwork CIDRs for the program to use
  + Note: This example is using structured configuration as per [Structured Configuration](https://www.pulumi.com/docs/intro/concepts/config/#structured-configuration)
  +
  + ```bash
  + $ pulumi config set --path 'subnet_cidr_blocks[0]' 172.1.0.0/16
  + $ pulumi config set --path 'subnet_cidr_blocks[1]' 172.2.0.0/16
  + ```
  +
  1. Run `pulumi up` to preview and deploy the changes:
  ```bash
  