Added Dockerfile.

Dockerfile

+FROM hseeberger/scala-sbt as cerebro-build
+COPY . /root/cerebro
+RUN cd cerebro && sbt stage
+
+FROM openjdk:jre-alpine
+ARG CEREBRO_VERSION=0.7.3
+COPY --from=cerebro-build /root/cerebro/target/universal/stage /opt/cerebro
+RUN apk add --no-cache --update bash
+WORKDIR /opt/cerebro
+EXPOSE 9000
+HEALTHCHECK CMD wget --quiet --spider http://localhost:9000/ || exit 1
+CMD ["bin/cerebro"]