initial Dockerfile added

Dockerfile

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+FROM alpine as helper
+ENV JTS3_SERVER_MOD_VERSION=6.5.7
+RUN wget -O JTS3ServerMod.zip "https://www.stefan1200.de/downloads/JTS3ServerMod_${JTS3_SERVER_MOD_VERSION}.zip" && unzip JTS3ServerMod.zip && mv JTS3ServerMod/changelog.txt JTS3ServerMod/readme.txt JTS3ServerMod/readme_deutsch.txt JTS3ServerMod/documents
+
+FROM alpine
+COPY --from=helper /JTS3ServerMod /JTS3ServerMod
+RUN apk add --no-cache openjdk8-jre-base
+WORKDIR /JTS3ServerMod
+CMD java -jar JTS3ServerMod.jar