Add Docker workflow support #3460

* Use a multi-stage build to reduce final image size.
* Run 'quicktest' make target before building.
* Built binary won't run on Alpine unless statically linked.

Dockerfile

@@ -0,0 +1,21 @@
+FROM golang AS builder
+
+COPY . /go/src/github.com/rclone/rclone/
+WORKDIR /go/src/github.com/rclone/rclone/
+
+RUN make quicktest
+RUN \
+  CGO_ENABLED=0 GOOS=linux GOARCH=amd64 \
+  make
+RUN ./rclone version
+
+# Begin final image
+FROM alpine:latest
+
+RUN apk --no-cache add ca-certificates
+
+WORKDIR /root/
+
+COPY --from=builder /go/src/github.com/rclone/rclone/rclone .
+
+ENTRYPOINT [ "./rclone" ]