Add dockerfile

Fixes komkom#4

Dockerfile

@@ -0,0 +1,18 @@
+FROM golang:1.16-alpine AS build
+
+# get the latest security updates
+# https://github.com/hadolint/hadolint/issues/562
+RUN apk --no-cache upgrade
+
+WORKDIR /go/src/app
+COPY . .
+
+# build a static binary for running from scratch
+# https://github.com/jeremyhuiskamp/golang-docker-scratch
+RUN go get -d -v ./...; \
+CGO_ENABLED=0 go install -ldflags '-extldflags "-static"' -tags timetzdata -v ./...
+
+FROM scratch
+COPY --from=build /go/bin/cmd /app
+
+CMD ["/app"]