Add dockerfile (#10)

* Adds a dockerfile, so that packet-headers can show up on dockerhub

Dockerfile

@@ -0,0 +1,16 @@
+# Build packet-headers
+FROM golang:1.12-alpine as build
+RUN apk --no-cache add libpcap-dev git gcc libc-dev
+COPY . /go/src/github.com/m-lab/packet-headers
+WORKDIR /go/src/github.com/m-lab/packet-headers
+RUN go get -v \
+      -ldflags "-X github.com/m-lab/go/prometheusx.GitShortCommit=$(git log -1 --format=%h)" \
+      .
+RUN chmod a+rx /go/bin/packet-headers
+
+# Put it in its own image.
+FROM alpine
+RUN apk --no-cache add libpcap
+COPY --from=build /go/bin/packet-headers /packet-headers
+WORKDIR /
+ENTRYPOINT ["/packet-headers"]