Dockerize the app

Dockerfile

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+FROM golang:1.11-alpine
+
+WORKDIR /app
+
+RUN apk add git && \
+    go get -u -v gitlab.com/pztrn/fastpastebin/cmd/fastpastebin
+
+FROM alpine:3.10
+LABEL maintainer "Stanislav N. <pztrn@pztrn.name>"
+
+COPY --from=0 /go/bin/fastpastebin /app/fastpastebin
+COPY examples/fastpastebin.yaml.docker /app/fastpastebin.yaml
+
+EXPOSE 25544
+ENTRYPOINT [ "/app/fastpastebin", "-config", "/app/fastpastebin.yaml" ]