note issues with AWS/GitHub at time of release (#232)

Author: baronfel

docs/RegistryAuthentication.md

@@ -31,15 +31,18 @@ All of the above mechanisms are supported by this package. When we push or pull
 The following registries have been explicitly tested:
 
 * Azure Container Registry*
-* AWS Elastic Container Registry
-* GitHub Package Registry
 * GitLab Container Registry
 * Google Cloud Artifact Registry
 * Quay.io
 
 ## Known-unsupported registries
 
 * Docker Hub
+  * needs changes to the code to differentiate between pushing to a local daemon and the remote hub
+* AWS Elastic Container Registry
+  * blob upload is canceled by ECR, unknown reason
+* GitHub Package Registry
+  * blob upload is canceled by the registry, unknown reason
 
 ## Notes for specific registries