update readme.md for all samples

Signed-off-by: Anca Iordache <anca.iordache@docker.com>

samples/nginx-golang/backend/Dockerfile

@@ -0,0 +1,11 @@
+FROM golang:1.13 AS build
+
+WORKDIR /compose/hello-docker
+COPY main.go main.go
+RUN CGO_ENABLED=0 go build -o backend main.go
+
+FROM scratch
+COPY --from=build /compose/hello-docker/backend /usr/local/bin/backend
+CMD ["/usr/local/bin/backend"]
+
+