Add Dockerfile and refine Makefile.

Dockerfile

@@ -0,0 +1,6 @@
+FROM alpine
+
+ARG ARCH
+EXPOSE 9550
+
+COPY dist/v2ray-exporter_linux_${ARCH} /usr/bin/v2ray-exporter

Makefile

@@ -1,10 +1,22 @@
-LAST_TAG  = $(shell git describe --tags --abbrev=0 HEAD)
-COMMIT = $(shell git rev-parse --short HEAD)
-FULL_COMMIT = $(shell git rev-parse HEAD)
+LAST_TAG      = $(shell git describe --tags --abbrev=0 HEAD)
+COMMIT        = $(shell git rev-parse --short HEAD)
+FULL_COMMIT   = $(shell git rev-parse HEAD)
 RELEASE_NOTES = $(shell git log ${LAST_TAG}..HEAD --oneline --decorate)
-DATE = $(shell date +%Y-%m-%d)
+DATE          = $(shell date +%Y-%m-%d)
 
-build:
+lint:
+	golangci-lint run *.go
+
+release_notes:
+	@echo "${RELEASE_NOTES}"
+
+before_build:
+	go get github.com/mitchellh/gox
+
+check_tag:
+	test ! -z "${TAG}"
+
+build: check_tag
 	gox -verbose \
 	    -output "dist/{{.Dir}}_{{.OS}}_{{.Arch}}" \
 	    -osarch "linux/amd64 linux/arm64 linux/arm darwin/amd64 windows/amd64" \
@@ -13,15 +25,10 @@ build:
 	              -X main.buildVersion=${LAST_TAG}" \
 	    ./...
 
-before_build:
-	go get github.com/mitchellh/gox
-
-lint:
-	golangci-lint run *.go
-
-release_notes:
-	@echo "${RELEASE_NOTES}"
-
 release: build
-	test ! -z "${TAG}"
 	@ghr -u wi1dcard -b "${RELEASE_NOTES}" -c "${FULL_COMMIT}" "${TAG}" dist/
+
+docker_build: build
+	docker build --build-arg ARCH=amd64 -t "wi1dcard/v2ray-exporter:${TAG}" .
+	docker build --build-arg ARCH=arm64 -t "wi1dcard/v2ray-exporter:${TAG}-arm64" .
+	docker build --build-arg ARCH=arm -t "wi1dcard/v2ray-exporter:${TAG}-arm" .