add buildx mutli-arch example and additional feature descriptions

06-building-container-images/Makefile

@@ -23,6 +23,18 @@ build-sample:
 		-f Dockerfile.sample \
 		.
 
+.PHONY: build-multiarch
+build-multiarch:
+	# Requires having container registry to push to
+	# Here it uses https://hub.docker.com/r/sidpalas/multi-arch-test
+	docker buildx build \
+		--platform linux/amd64,linux/arm64,linux/arm/v7 \
+		--secret id=secret.txt,src=local-secret.txt \
+		-t sidpalas/multi-arch-test:latest \
+		-f Dockerfile.sample \
+		--push \
+		.
+
 define ENTRYPOINT_CMD_DESCRIPTION
 ##############################