add official Dockerfile (#104)

Dockerfile

@@ -0,0 +1,33 @@
+FROM golang:1.11.10-alpine as builder
+MAINTAINER FullStory Engineering
+
+# currently, a module build requires gcc (so Go tool can build
+# module-aware versions of std library; it ships only w/ the
+# non-module versions)
+RUN apk update && apk add --no-cache ca-certificates git gcc g++ libc-dev
+# create non-privileged group and user
+RUN addgroup -S grpcurl && adduser -S grpcurl -G grpcurl
+
+WORKDIR /tmp/fullstorydev/grpcurl
+# copy just the files/sources we need to build grpcurl
+COPY VERSION *.go go.* /tmp/fullstorydev/grpcurl/
+COPY cmd /tmp/fullstorydev/grpcurl/cmd
+# and build a completely static binary (so we can use
+# scratch as basis for the final image)
+ENV CGO_ENABLED=0
+ENV GOOS=linux
+ENV GOARCH=amd64
+ENV GO111MODULE=on
+RUN go build -o /grpcurl \
+    -ldflags "-w -extldflags \"-static\" -X \"main.version=$(cat VERSION)\"" \
+    ./cmd/grpcurl
+
+# New FROM so we have a nice'n'tiny image
+FROM scratch
+WORKDIR /
+COPY --from=builder /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/ca-certificates.crt
+COPY --from=builder /etc/passwd /etc/passwd
+COPY --from=builder /grpcurl /bin/grpcurl
+USER grpcurl
+
+ENTRYPOINT ["/bin/grpcurl"]