Add dockerized version

Signed-off-by: Knut Ahlers <knut@ahlers.me>

Dockerfile

@@ -0,0 +1,30 @@
+FROM golang:alpine as builder
+
+COPY . /go/src/github.com/Luzifer/automail
+WORKDIR /go/src/github.com/Luzifer/automail
+
+RUN set -ex \
+ && apk add --update git \
+ && go install \
+      -ldflags "-X main.version=$(git describe --tags --always || echo dev)" \
+      -mod=readonly
+
+FROM alpine:latest
+
+ENV CONFIG=/data/config.yml \
+    STORAGE_FILE=/data/automail_store.yml
+
+LABEL maintainer "Knut Ahlers <knut@ahlers.me>"
+
+RUN set -ex \
+ && apk --no-cache add \
+      ca-certificates
+
+COPY --from=builder /go/bin/automail /usr/local/bin/automail
+
+VOLUME ["/data"]
+
+ENTRYPOINT ["/usr/local/bin/automail"]
+CMD ["--"]
+
+# vim: set ft=Dockerfile: