fix: [#34] added multiple copy of the config file (#37)

registry/Dockerfile

@@ -4,7 +4,10 @@ RUN apk update && \
     apk upgrade
 # A custom config file is needed to disable default cache
 # By default the cache is "blobdescriptor: inmemory"
-# The config-example.yml file of this repo disables it
+# The config-example.yml file of this repo can be found at:
 # https://github.com/distribution/distribution-library-image
+# File is copied to two different locations to keep
+# compatibility with registry:2.x and registry:3.x
 COPY ./config-example.yml /etc/docker/registry/config.yml
+COPY ./config-example.yml /etc/distribution/config.yml
 COPY ./backup-registry /var/lib/registry