aws-ecr-assets: there's no description about CDK_DOCKER environment variable

[ymotongpoo]

Describe the issue

Though there are cases where the local machine doesn't have docker command but has podman, nerdctl or finch, the document of aws-ecr-assets doesn't mention that it supports Docker CLI compatible commands with CDK_DOCKER. This information is not available either from the document[1] or from the error message[2].

[1] https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.aws_ecr_assets-readme.html

[2]

ContainerAassetsStack: fail: Unable to execute 'docker' in order to build a container asset. Please install 'docker' and try again.

Links

https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.aws_ecr_assets-readme.html#images-from-dockerfile

[khushail]

Thanks @ymotongpoo for reporting this issue and submitting a PR for the same. Its always helpful to have clear documentation and your PR adds-on on that enhancement about CDK_DOCKER. Appreciate your efforts!