Update README with customizations!

Signed-off-by: Dave Tucker <dt@docker.com>

README.md

@@ -62,6 +62,41 @@ A simple Minecraft Docker client, to visualize and manage Docker containers.
 
 ![Dockercraft](https://github.com/docker/dockercraft/raw/master/docs/img/landscape.png?raw=true)
 
+## Customizing Dockercraft
+
+Do you find the plains too plain?
+If so, you are in luck!
+
+Dockercraft can be customised to use any of the [Biomes](https://github.com/cuberite/cuberite/blob/7f8a4eb7264a12ca2035b4e4d412485e01f309d4/src/BiomeDef.cpp#L17) and [Finishers](https://github.com/cuberite/cuberite/blob/7f8a4eb7264a12ca2035b4e4d412485e01f309d4/src/Generating/ComposableGenerator.cpp#L299) supported by Cuberite!
+
+You can pass these additional arguments to your `docker run` command:
+```
+docker run -t -i -d -p 25565:25565 \
+    -v /var/run/docker.sock:/var/run/docker.sock \
+    --name dockercraft \
+    gaetan/dockercraft <biome> <groundlevel> <sealevel> <finishers>
+```
+
+Here are some examples:
+
+**Do you long for the calm of the oceans?**
+![oceans](https://github.com/docker/dockercraft/raw/master/docs/img/ocean.png?raw=true)
+
+Try `Ocean 50 63`, or for a more frozen alternative, `FrozenOcean 50 63 Ice`
+
+**Or perhaps the heat of the desert?**
+![desert](https://github.com/docker/dockercraft/raw/master/docs/img/desert.png?raw=true)
+
+Then `Desert 63 0 DeadBushes` is what you need
+
+**Are you pining for the... Pines?**
+![forest](https://github.com/docker/dockercraft/raw/master/docs/img/forest.png?raw=true)
+We have you covered. Try `Forest 63 0 Trees`
+
+**Or maybe you are looking for fun and games?**
+![jungle](https://github.com/docker/dockercraft/raw/master/docs/img/jungle.png?raw=true)
+If so, Welcome to the Jungle. `Jungle 63 0 Trees`
+
 ## Upcoming features
 
 This is just the beginning for Dockercraft! We should be able to support a lot more Docker features like: