L2SS-822: add documentation

docker-compose/README.md

@@ -39,6 +39,23 @@ registry and uploaded to our own using matching tags.
 
 Services, same mechanism as devices.
 
+### HDB++ image updates
+
+The hdbpp Docker image is used as a base image for the hdbppts-cm (ConfigurationManager) and hdbppts-es (EventSubscriber)
+images. If one is developing on a branch and any updates is made in hdbpp/Dockerfile, those won't be automatically picked up from hdbppts-cm and hdbppts-es, because the argument SOURCE_IMAGE in the docker-compose yml file always refers to the remote hdbpp image in the repository. 
+
+A temporary workaround for locally testing on these archiving containers is the following:
+
+- Stop and remove any running hdbpp* container
+- In the archiver-timescale.yml file, replace the hdbppts-cm and hdbppts-es SOURCE_IMAGE tag 'latest' with the branch name 
+(e.g. SOURCE_IMAGE: ${LOCAL_DOCKER_REGISTRY_HOST}/${LOCAL_DOCKER_REGISTRY_USER}/hdbpp:l2ss-new-branch)
+- Rebuild all the hdbpp* container (make build hdbpp hdbppts-cm hdbppts-es), and then start them
+- Test the new features
+
+After the branch has been correctly developed, tested, the merge has been approved, and the new images have been built on the repository:
+- Put back 'latest' tag on the archiver-timescale.yml file, replacing the branch name
+- Merge on master 
+
 ### Setup and maintenance
 
 All behavioral logic to orchestrate change detection and image pushing can be