Revert "Remove entrypoint and configf file argument."

This reverts commit 9cbb3ad.

Author: hadrianvalentine

Dockerfile

@@ -27,4 +27,6 @@ RUN bundle install --jobs 4 --retry 3
 VOLUME "${GEMSTASH_HOME}/data"
 
 EXPOSE 9292
-CMD ["bundle", "exec", "gemstash", "start", "--no-daemonize"]
+USER ${GEMSTASH_USER}:${GEMSTASH_USER}
+ENTRYPOINT ["tini", "--"]
+CMD ["bundle", "exec", "gemstash", "start", "--no-daemonize", "--config-file=config.yml.erb"]