add a simple docker example

Former-commit-id: cacfa3ad903ce542ce455cb2298c40639c645d3c

_examples/docker/Dockerfile

@@ -0,0 +1,15 @@
+# docker build -t myapp . 
+# docker run --rm -it -p 8080:8080 myapp:latest
+FROM golang:latest AS builder
+RUN apt-get update
+ENV GO111MODULE=on \
+    CGO_ENABLED=0 \
+    GOOS=linux \
+    GOARCH=amd64
+WORKDIR /go/src/app
+COPY . /go/src/app
+RUN go install
+
+FROM scratch
+COPY --from=builder /go/bin/app .
+ENTRYPOINT ["./app"]