Added Makefile mods, Dockerfile for demo

Dockerfile

+FROM golang:1.13.1
+
+WORKDIR /gotty
+COPY . /gotty
+RUN CGO_ENABLED=0 make
+
+FROM alpine:latest
+
+RUN apk update && \
+    apk upgrade && \
+    apk --no-cache add ca-certificates && \
+    apk add bash
+WORKDIR /root
+COPY --from=0 /gotty/gotty /usr/bin/
+CMD ["gotty",  "-w", "bash"]

Makefile

@@ -78,3 +78,5 @@ shasums:
 
 
 release:
 release:
 	ghr -c ${GIT_COMMIT} --delete --prerelease -u yudai -r gotty pre-release ${OUTPUT_DIR}/dist
 	ghr -c ${GIT_COMMIT} --delete --prerelease -u yudai -r gotty pre-release ${OUTPUT_DIR}/dist
+clean:
+	rm -fr gotty