Added some documentation to README.md

README.md

@@ -19,7 +19,7 @@ Run
 ---
 
 ```bash
-docker run -p 2181:2181 -p 9092:9092 --env ADVERTISED_HOST=`docker-machine ip \`docker-machine active\`` --env ADVERTISED_PORT=9092 spotify/kafka
+docker run -p 2181:2181 -p 9092:9092 --env ADVERTISED_HOST=`docker-machine ip \`docker-machine active\`` --env ADVERTISED\_PORT=9092 spotify/kafka
 ```
 
 ```bash
@@ -32,6 +32,20 @@ export ZOOKEEPER=`docker-machine ip \`docker-machine active\``:2181
 kafka-console-consumer.sh --zookeeper $ZOOKEEPER --topic test
 ```
 
+Optional ENV Variables
+----------------------
+
+The container supports a few optional ENV variables that can be used to configure
+the Kafka instance. They are as follows:
+
+- ``ADVERTISED_HOST``: the external ip for the container
+-  ``ADVERTISED_PORT``: the external port for Kafka, e.g. 9092
+- ``ZK_CHROOT``: the zookeeper chroot that's used by Kafka (without / prefix), e.g. "kafka"
+- ``LOG_RETENTION_HOURS``: the minimum age of a log file in hours to be eligible for deletion (default is 168, for 1 week)
+- ``LOG_RETENTION_BYTES``: configure the size at which segments are pruned from the log, (default is 1073741824, for 1GB)
+- ``NUM_PARTITIONS``: configure the default number of log partitions per topic
+
+
 Running the proxy
 -----------------