Improve Dockerfile and README

Author: patzly

Dockerfile

@@ -5,6 +5,6 @@ RUN apt-get update && apt-get install -y libxrender1 libxtst6 libxi6
 WORKDIR /app
 ADD . /app
 
-ENV HEADLESS=false
+ENV HEADLESS=true
 
 ENTRYPOINT sbt -Djava.awt.headless=$HEADLESS run

README.md

@@ -37,10 +37,10 @@ Then you can run the game by executing the following command:
 docker run -it set-game-scala
 ```
 
-On macOS, you need to run the following command instead to disable the GUI as macOS does not support X11:
+On Linux, you can run the following command instead to enable the GUI:
 
 ```bash
-docker run -it -e HEADLESS=true set-game-scala
+docker run -it -e HEADLESS=false -e DISPLAY=$DISPLAY -v /tmp/.X11-unix:/tmp/.X11-unix set-game-scala
 ```
 
 ## License