Update VPC instructions
Update VPC instructions

I have this lambda code successfully running inside a VPC.

You can, as the README said, add a NAT gateway, but that [costs extra
money](https://aws.amazon.com/vpc/pricing/) - you can instead create
a [VPC endpoint for S3](https://docs.aws.amazon.com/vpc/latest/privatelink/vpc-endpoints-s3.html)
within your VPC, and add a security group egress rule that allows
traffic from the security group to the appropriate S3 prefixlist based
on the region, if you are blocking egress by default.

You can find the appropriate PrefixList for a region via aws-cli:

`aws ec2 describe-prefix-lists --region eu-west-2`

jameshy/pgdump-aws-lambda,jameshy/pgdump-aws-lambda