Add docker image building

Dockerfile

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+FROM golang:alpine AS build-env
+
+ADD . /src
+RUN apk --no-cache add git gcc musl-dev
+RUN cd /src && go get -d && go build -o linkinfo service/main.go
+
+FROM alpine
+
+MAINTAINER Tyler Stuyfzand <tyler@tystuyfzand.com>
+
+EXPOSE 53
+
+RUN apk --no-cache add tini
+ENTRYPOINT ["/sbin/tini", "-g", "--"]
+CMD ["linkinfo"]
+
+COPY --from=build-env /src/linkinfo /usr/local/bin/linkinfo
+RUN chmod +x /usr/local/bin/linkinfo