Update upgrading_to_v35.0.md

Author: apeabody

docs/upgrading_to_v35.0.md

@@ -2,4 +2,4 @@
 The v35.0 release of *kubernetes-engine* is a backwards incompatible release.
 
 ### Google Cloud Platform Provider upgrade
-The Terraform Kubernetes Engine Module now requires version 6 of the Google Cloud Platform Providers.
+The Terraform Kubernetes Engine Module now requires version 6 of the Google Cloud Platform Providers.  See the [Terraform Google Provider 6.0.0 Upgrade Guide](https://registry.terraform.io/providers/hashicorp/google/latest/docs/guides/version_6_upgrade) for more details.