Add dockerfile and CI

Dockerfile

@@ -0,0 +1,12 @@
+FROM golang:alpine AS build
+ADD . /go/src/sumika/
+ARG GOARCH=amd64
+ENV GOARCH ${GOARCH}
+ENV CGO_ENABLED 0
+WORKDIR /go/src/sumika
+RUN go build .
+
+FROM alpine
+COPY --from=build /go/src/sumika /bin/sumika
+WORKDIR /data
+CMD sumika