Added Dockerfile which builds and packages s3sync (larrabee#28)

- build with golang:1.13 which based on debian:10
- package with image based on debian:10

Author: sergey-shambir

.dockerignore

@@ -0,0 +1,6 @@
+# Binary
+s3sync
+
+# Vendor dir
+vendor/
+dist/

Dockerfile

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+# Build in Docker container
+FROM golang:1.13 as builder
+
+COPY . /src/s3sync
+WORKDIR /src/s3sync
+RUN go mod vendor && \
+    go build -o /usr/local/bin/s3sync ./cli
+
+# Create s3sync image
+FROM debian:10
+COPY --from=builder /usr/local/bin/s3sync /usr/local/bin/s3sync