docs: add errata summary between repo and published guide. (#219)

Author: rjerrems

ERRATA.md

@@ -0,0 +1,20 @@
+## Errata Summary
+This is an overview of the delta between the example foundation repository and the [Google Cloud security foundations guide](https://services.google.com/fh/files/misc/google-cloud-security-foundations-guide.pdf), including code discrepancies and notes on future automation. This document will be updated as new code is merged.
+
+### Code Discrepancies
+
+##### Labeling
+- The guide defines vpc-type for shared, service, float, nic, and peer projects. It does not define a vpc-type for Jenkins agents (vpc-b-jenkinsagents), the DNS Hub (vpc-dns-hub) and projects created in 4-projects.
+This will be addressed in the next version of the whitepaper.
+
+##### Naming
+- The Service Account & Storage bucket naming are not aligned to the blueprint guide. Naming will be modified accordingly in a future release.
+
+##### Pre-deployment Check
+- Terraform Validator, described in Section 5.2, is not implemented in the Cloud Build and Jenkins pipelines, but will be integrated in a future release.
+
+### Notes
+- The BigQuery Log Detection solution, described in Section 10 will be integrated in a future release.
+- Splunk log integration will be integrated in a future release.
+- Cloud Asset Inventory will be integrated in a future release.
+- The unallocated IP address space in the Shared VPC networks, described in Section 7.3, is currently being used by Private Service Networking in this release.

README.md

@@ -243,6 +243,10 @@ Development happens on feature/bugfix branches (which can be named `feature/new-
 
 Once validated in `development`, changes can be promoted to `non-production` by opening a PR/MR targeting the `non-production` branch and merging them.  Similarly changes can be promoted from `non-production` to `production`.
 
+## Errata Summary
+
+Refer to the [Errata Summary](./ERRATA.md) for an overview of the delta between the example foundation repository and the [Google Cloud security foundations guide](https://services.google.com/fh/files/misc/google-cloud-security-foundations-guide.pdf).
+
 ## Contributing
 
 Refer to the [contribution guidelines](./CONTRIBUTING.md) for