fix unit and add new example to the documentation for rancher cluster v2

[jiaqiluo]

This is a follow-up PR for https://github.com/rancher/terraform-provider-rancher2/pull/1300

This PR contains the following changes:

• fixes the unit in the example for resource_requirement
• adds an example for setting the IPv4/IPv6 network CIDRs to use for pod IPs and service IPs in an RKE2/K3s cluster