Docker: add arm32v6 Dockerfile

Dockerfile.arm32v6

@@ -0,0 +1,24 @@
+FROM arm32v6/golang:1.9-alpine as builder
+
+COPY . /go/src/mumble.info/grumble
+
+WORKDIR /go/src/mumble.info/grumble
+
+RUN apk add --no-cache git \
+  && go get -v -t ./... \
+  && go build mumble.info/grumble/cmd/grumble \
+  && go test -v ./...
+
+FROM arm32v6/golang:1.9-alpine
+
+COPY --from=builder /go/bin /go/bin
+
+ENV DATADIR /data
+
+RUN mkdir /data
+
+WORKDIR /data
+
+VOLUME /data
+
+ENTRYPOINT [ "/go/bin/grumble", "--datadir", "/data", "--log", "/data/grumble.log" ]