more docs.

README.md

@@ -1,3 +1,9 @@
+## Objective
+
+I would like to be able to use local (or registry) based build cache storage backends within my AWS CDK projects. AWS CDK creates an ECR repository as part of it's `bootstrap` process that is immutable by default. As it stands, you can not push anything to this immutable ECR repository at all once you've enabled the containerd image store in Docker.
+
+## Reproducing the issue
+
 To reproduce the issue within AWS ECR:
 
 Enable the `containerd image store` as per https://docs.docker.com/build/cache/backends/ by adding the following to the Docker features:
@@ -10,6 +16,12 @@ Enable the `containerd image store` as per https://docs.docker.com/build/cache/b
 
 ref: https://docs.docker.com/engine/storage/containerd/#enable-containerd-image-store-on-docker-engine
 
+Create an ECR repository:
+
+```
+aws ecr create-repository --image-tag-mutability IMMUTABLE --repository-name tester
+```
+
 Sign in to AWS ECR:
 
 ```
@@ -19,17 +31,17 @@ aws ecr get-login-password --region us-east-2 | docker login --username AWS --pa
 Build this image:
 
 ```
-docker build -t 211125654114.dkr.ecr.us-east-2.amazonaws.com/test-immutable:bar .
+docker build -t 211125654114.dkr.ecr.us-east-2.amazonaws.com/tester:bar .
 ```
 
 Push this image:
 
 ```
-docker push 211125654114.dkr.ecr.us-east-2.amazonaws.com/test-immutable:bar
+docker push 211125654114.dkr.ecr.us-east-2.amazonaws.com/tester:bar
 ```
 
 This yields:
 
 ```
-failed commit on ref "manifest-sha256:b1046f6218c477a57f78da412bdf0e9225359b4f46f01a30f7929a3517a59e5f": unexpected status from PUT request to https://211125654114.dkr.ecr.us-east-2.amazonaws.com/v2/test-immutable/manifests/bar: 400 Bad Request
+failed commit on ref "manifest-sha256:c464ef84ed0decc225c0913deec2153b8ef013b195ece219f890a05e96d86e1f": unexpected status from PUT request to https://211125654114.dkr.ecr.us-east-2.amazonaws.com/v2/tester/manifests/bar: 400 Bad Request
 ```