Updated README.md to reflect additional requirements of awscli and jq…

…, as

well as providing information regarding a Docker image that has this all
in place.

README.md

@@ -3,6 +3,16 @@
 Run the AWS CLI, with the ability to run under an assumed role, to access resources and properties missing from the
 Terraform AWS Provider.
 
+# Requirements
+
+This module requires a couple of additional resources to operate successfully.
+
+1. Amazon Web Service Command Line Interface (awscli)  
+   This is available in several forms [here](https://aws.amazon.com/cli/).
+
+2. JSON processor (jq)  
+   This is available [here](https://stedolan.github.io/jq/).
+
 # Examples
 
 ## 1. Get the desired capacity of an autoscaling group.
@@ -69,3 +79,38 @@ module "current_desired_capacity" {
 | result | The output of the AWS CLI command |
 
 <!-- END OF PRE-COMMIT-TERRAFORM DOCS HOOK -->
+
+# Docker
+
+To help with getting this running in a pipeline that uses Docker, the image [digiticketsgroup/terraforming](https://hub.docker.com/repository/docker/digiticketsgroup/terraforming) has Terraform, AWSCLI, and jq all ready to go.
+
+If you want to build or adapt your own image, then the Dockerfile below is how that image has been built.
+
+```Dockerfile
+# Based upon https://github.com/aws/aws-cli/blob/2.0.10/docker/Dockerfile
+FROM amazonlinux:2 as installer
+ARG TERRAFORM_VERSION
+RUN yum update -y \
+  && yum install -y unzip \
+  && curl https://awscli.amazonaws.com/awscli-exe-linux-x86_64.zip -o awscli-exe-linux-x86_64.zip \
+  && unzip awscli-exe-linux-x86_64.zip \
+  # The --bin-dir is specified so that we can copy the
+  # entire bin directory from the installer stage into
+  # into /usr/local/bin of the final stage without
+  # accidentally copying over any other executables that
+  # may be present in /usr/local/bin of the installer stage.
+  && ./aws/install --bin-dir /aws-cli-bin/ \
+  && curl "https://releases.hashicorp.com/terraform/${TERRAFORM_VERSION}/terraform_${TERRAFORM_VERSION}_linux_amd64.zip" -o terraform.zip \
+  && unzip terraform.zip
+
+FROM amazonlinux:2
+COPY --from=installer /usr/local/aws-cli/ /usr/local/aws-cli/
+COPY --from=installer /aws-cli-bin/ /usr/local/bin/
+COPY --from=installer terraform /usr/bin/
+RUN yum update -y \
+  && yum install -y less groff jq \
+  && yum clean all
+
+ENTRYPOINT ["/bin/sh"]
+```
+