docs/contributing: undocumented new region values (#20758)

#12967
#13061
#12976

docs/contributing/contribution-checklists.md

@@ -904,7 +904,9 @@ of this guide as appropriate.
 
 While region validation is automatically added with SDK updates, new regions
 are generally limited in which services they support. Below are some
-manually sourced values from documentation.
+manually sourced values from documentation. Amazon employees can code search
+previous region values to find new region values in internal packages like
+RIPStaticConfig if they are not documented yet.
 
 - [ ] Check [Elastic Load Balancing endpoints and quotas](https://docs.aws.amazon.com/general/latest/gr/elb.html#elb_region) and add Route53 Hosted Zone ID if available to `aws/data_source_aws_elb_hosted_zone_id.go`
 - [ ] Check [Amazon Simple Storage Service endpoints and quotas](https://docs.aws.amazon.com/general/latest/gr/s3.html#s3_region) and add Route53 Hosted Zone ID if available to `aws/hosted_zones.go`