Update Getting Started

[Nayels]

Usage section is not up to date anymore.

module "gce-ilb" {
  source       = "terraform-google-modules/lb-internal/google"
 ... 
}

It gives the following error:

Error: Module not found

Module "gce-ilb" (from main.tf:106) cannot be found in the module registry at
registry.terraform.io.

Should be:

module "gce-ilb" {
  source       = "GoogleCloudPlatform/lb-internal/google"
 ... 
}