chore: creating initial upgrade file (#471)

* chore: Migrating README file to new template format.

* chore: Creating initial file

* fix lint

* improve language around fw rules

* Apply suggestions from code review

Co-authored-by: Daniel Andrade <[email protected]>

* Update README.md

* Update upgrading_to_v2.0.md

* Update upgrading_to_v2.0.md

* chore: removed trailing whitespace

Co-authored-by: Bharath KKB <[email protected]>
Co-authored-by: Daniel Andrade <[email protected]>

Author: 3 people

docs/upgrading_to_v2.0.md

@@ -0,0 +1,29 @@
+# Upgrade Guidance
+
+Before moving forward with adopting components of V2, please review the list of
+breaking changes below. You can find a list of all changes in the
+[Changelog](https://github.com/terraform-google-modules/terraform-example-foundation/blob/master/CHANGELOG.md).
+
+**Note:** There is no in-place upgrade path from v1 to v2.
+
+## Breaking Changes
+
+-  The repo now requires Terraform version 0.13 (minimum). For v1 the minimum version was
+   0.12.x.
+-  V2 introduces a new alternative hub-and-spoke network architecture,
+   described in Section 7.2 of the [Google Cloud security foundations guide](https://services.google.com/fh/files/misc/google-cloud-security-foundations-guide.pdf).
+-  In V2, the infrastructure pipeline has transitioned from using
+[Google Container Registry](https://cloud.google.com/container-registry/docs) (GCR) to using [Google Artifact Registry](https://cloud.google.com/artifact-registry/docs). Artifact
+   Registry extends the capabilities of GCR as outlined
+   [here](https://cloud.google.com/artifact-registry/docs/transition/transition-from-gcr#compare).
+-  Some [VPC firewall rules](https://cloud.google.com/vpc/docs/firewalls) have been replaced with [Hierarchical firewall policy rules](https://cloud.google.com/vpc/docs/firewall-policies), which provides the same functionality of allowing or denying connections to or from your virtual machine instances but allowing enforcement of consistent firewall policies across your organization.
+
+## Steps to upgrade codebase
+
+**Note:** When you run `terraform apply`, expect resources to be deleted and recreated. Be sure
+ to monitor errors during the `terrform apply` process.
+
+1. If you have already forked V1 in your private repository, you can
+   manually merge changes from V2 into your modified version of V1.
+1. If you have not made modifications to V1, you can upgrade the existing
+   fork to V2