Add link to documentation for private ECR access from private subnet with no NAT gateway

[emilebourquin]

TemplateID: (fargate/service-cluster-alb)
Region: (us-west-1)

For Fargate Services in a private subnet, with no access to a NAT gateway, several VPC endpoints (aka PrivateLink) need to be created so that the service can retrieve images from a private ECR repositry. The page at https://docs.aws.amazon.com/AmazonECR/latest/userguide/vpc-endpoints.html details what those VPC endpoints should be. Perhaps this page could be mentioned in the documentation.

[michaelwittig]

Sounds like a good plan.
You can find the docs under ./docs/fargate.md in this repo.