Add Dockerfile

Dockerfile

+FROM golang:1.11.1-alpine3.7 as builder
+LABEL maintainer="Mike Jones"
+
+RUN mkdir -p /go/src/git.netsplit.uk/stella-irc/modlastfm
+COPY . /go/src/git.netsplit.uk/stella-irc/modlastfm
+
+RUN apk update && apk upgrade && \
+    apk add --no-cache git gcc musl-dev
+
+WORKDIR /go/src/git.netsplit.uk/stella-irc/modlastfm
+
+RUN go get ./... && \
+    CGO_ENABLED=0 GOOS=linux GOARCH=amd64 \
+    go build -o /opt/modlastfm cmd/modlastfm/main.go && \
+    apk del --purge git gcc musl-dev && \
+    rm -rf /go/bin /go/pkg /var/cache/apk/*
+
+RUN chmod +x /opt/modlastfm
+
+FROM scratch
+
+COPY --from=builder /opt /opt
+
+ENTRYPOINT ["/opt/modlastfm"]