Added a Dockerfile to build the tool in a docker container

Use an alpine base image. The image size is 40MB.

.dockerignore

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+# Binaries for programs and plugins
+*.exe
+*.dll
+*.so
+*.dylib
+ethdo
+
+# Test binary, build with `go test -c`
+*.test
+
+# Output of the go coverage tool, specifically when used with LiteIDE
+*.out
+coverage.html
+
+# Project-local glide cache, RE: https://github.com/Masterminds/glide/issues/736
+.glide/
+
+# Vim
+*.sw?
+
+# Local TODO
+TODO.md
+
+Dockerfile

Dockerfile

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+FROM golang:1.14.2-alpine3.11 as builder
+
+RUN apk add build-base
+
+WORKDIR /app
+
+COPY go.mod go.sum ./
+
+RUN go mod download
+
+COPY . .
+
+RUN go build
+
+FROM alpine:3.11
+
+RUN apk add libstdc++
+
+WORKDIR /app
+
+COPY --from=builder /app/ethdo /app
+
+ENTRYPOINT ["/app/ethdo"]