Add README.

README.md

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+# Factorio Docker image
+
+This image includes the headless build of Factorio with paths set to store data in the /data folder and configuration in the /config folder which can both be used as volumes.
+
+## Starting a server
+
+### Creating the savefile
+
+Before first start up you should make sure to create a save file for the server to load by running:
+
+    docker run --rm \
+        -v /path/to/data:/data \
+        -v /path/to/config:/config \
+        /opt/factorio/bin/x64/factorio --create /data/saves/my-save.zip
+
+After that you can use the givena volumes for running the server, for example using Docker Compose!
+
+### Example Docker Compose file
+
+```yaml
+version: "2"
+
+services:
+    factorio:
+        # The image to use, version number of the server can be used as a tag.
+        image: icedream/factorio:0.14.2
+
+        # Volumes to mount in
+        volumes:
+            - /path/to/data:/data
+            - /path/to/config:/config
+
+        # Optionally replace the command to run to configure further details
+        # or even make use of map generation or server settings files.
+        #command: /opt/factorio/bin/x64/factorio --start-server-load-latest --rcon-password somepassword
+```