Add entrypoint, -dir parameter

Dockerfile

@@ -6,6 +6,9 @@ RUN cd /go/src; go build -o sleeper
 
 FROM alpine
 
-COPY --from=builder /go/src/sleeper /sleeper
+ADD docker/entrypoint.sh /entrypoint.sh
+COPY --from=builder /go/src/sleeper /usr/bin/sleeper
 
-CMD ["/sleeper"]
+RUN chmod +x /entrypoint.sh
+
+ENTRYPOINT "/entrypoint.sh"