Add simple Dockerfile to run fritzbox_exporter as docker container

Dockerfile

@@ -0,0 +1,12 @@
+FROM golang:1.8-alpine
+
+ADD . $GOPATH/src/github.com/ndecker/fritzbox_exporter
+
+RUN apk add --no-cache git
+RUN go get -v github.com/ndecker/fritzbox_exporter
+
+EXPOSE 9133
+
+ENTRYPOINT ["fritzbox_exporter"]
+CMD [""]
+