Build: Fix Docker image

This has been broken ever since the upgrade to Java 11 and moving tracks
to server resources. Now it works again and is tested in CI to ensure it
won't break again.

.github/workflows/build.yml

@@ -32,3 +32,7 @@ jobs:
         run: sudo apt-get install -y genisoimage
       - name: Build with Maven
         run: mvn -B install --file pom.xml
+      - name: Build Docker image
+        uses: docker/build-push-action@v5
+        with:
+          tags: philippvk/minigolf:latest

Dockerfile

@@ -1,16 +1,15 @@
 #
 # Build stage
 #
-FROM maven:3.6.0-jdk-8-slim AS build
+FROM maven:3.9.7-eclipse-temurin-21 AS build
 COPY . /home/app/
 RUN mvn -f /home/app/pom.xml -pl server -am clean package
 
 #
 # Package stage
 #
-FROM openjdk:8-alpine
+FROM eclipse-temurin:21-alpine
 COPY --from=build /home/app/server/target/server-*.jar /home/minigolf/server.jar
-COPY tracks/ /home/minigolf/tracks/
 EXPOSE 4242
 WORKDIR /home/minigolf
 ENTRYPOINT ["java","-jar","server.jar"]

README.md

@@ -62,7 +62,13 @@ java -jar client.jar -server 192.168.1.7 -lang en_US # Replace IP with the one o
 
 #### Running Minigolf Server in Docker Container
 
-We provide an experimental Dockerfile for easy hosting of the server application. You can either build the image by yourself or download the pre-build images from [quay.io](https://quay.io/repository/philippvk/minigolf) via `docker pull quay.io/philippvk/minigolf:latest`.
+We provide an experimental Dockerfile for easy hosting of the server application. 
+You can either build and run the image:
+```sh
+docker build -t pfmg .
+docker run pfmg
+```
+or download the pre-built images from [quay.io](https://quay.io/repository/philippvk/minigolf) via `docker pull quay.io/philippvk/minigolf:latest`.
 
 Running the Editor is quite straightforward as it can be started like expected: `java -jar editor.jar`