Add CONTRIBUTING

Dockerfile

+# This file is a template, and might need editing before it works on your project.
+FROM maven:3.5-jdk-11 as BUILD
+
+COPY . /usr/src/app
+RUN mvn --batch-mode -f /usr/src/app/pom.xml clean package
+
+FROM openjdk:11-jdk
+ENV PORT 4567
+EXPOSE 4567
+COPY --from=BUILD /usr/src/app/target /opt/target
+WORKDIR /opt/target
+
+CMD ["/bin/bash", "-c", "find -type f -name '*-with-dependencies.jar' | xargs java -jar"]