Merge pull request terraform-google-modules#30 from crayfishx/docs/source

[docs] Change source reference in README to reflect registry source address

Author: morgante

README.md

@@ -14,7 +14,7 @@ There are multiple examples included in the [examples](./examples/) folder but s
 
 ```hcl
 module "gke" {
- source = "github.com/terraform-google-modules/terraform-google-kubernetes-engine?ref=v0.1.0"
+ source = "terraform-google-modules/kubernetes-engine/google"
  project_id = "<PROJECT ID>"
  name = "gke-test-1"
  region = "us-central1"
@@ -256,4 +256,4 @@ are as follows:
 is a compiled language so there is no standard linter.
 * Terraform - terraform has a built-in linter in the 'terraform validate'
 command.
-* Dockerfiles - hadolint. Can be found in homebrew
+* Dockerfiles - hadolint. Can be found in homebrew