add GHA CD via Dockerhub

Makefile

@@ -1,5 +1,8 @@
 # BEGIN-EVAL makefile-parser --make-help Makefile
 
+DOCKER_BASE_IMAGE = docker.io/ocrd/core:v2.69.0
+DOCKER_TAG = ocrd/nmalign
+
 .PHONY: help install
 help:
 	@echo ""
@@ -10,8 +13,12 @@ help:
 	@echo "    test     Run tests"
 	@echo "    clean    Remove copies/results in test/assets"
 	@echo ""
+	@echo "    docker  Build a Docker image $(DOCKER_TAG) from $(DOCKER_BASE_IMAGE)"
+	@echo ""
 	@echo "  Variables"
 	@echo ""
+	@echo "    PYTHON"
+	@echo "    DOCKER_TAG    Docker image tag of result for the docker target"
 
 # END-EVAL
 
@@ -40,6 +47,15 @@ test: test/assets models
 	ocrd-sbb-binarize -m test/assets/kant_aufklaerung_1784-page-region/data/mets.xml -g phys_0001 -I OCR-D-GT-SEG-REGION -O BIN -P model default -P operation_level region
 	ocrd-sbb-binarize -m test/assets/kant_aufklaerung_1784-page-region/data/mets.xml -g phys_0001 -I OCR-D-GT-SEG-REGION -O BIN2 -P model default-2021-03-09 -P operation_level region
 
+.PHONY: docker
+docker:
+	docker build \
+	--build-arg DOCKER_BASE_IMAGE=$(DOCKER_BASE_IMAGE) \
+	--build-arg VCS_REF=$$(git rev-parse --short HEAD) \
+	--build-arg BUILD_DATE=$$(date -u +"%Y-%m-%dT%H:%M:%SZ") \
+	-t $(DOCKER_TAG) .
+
+
 .PHONY: clean
 clean:
 	-$(RM) -fr test/assets