Update Hacking.md with mri instructions

HACKING.md

@@ -8,5 +8,23 @@
  * set port 2181
 * Start Kafka
   * Set properties file ```zookeeper.connect=localhost:2181```
+
+You can also use a docker instance like this one : https://github.com/spotify/docker-kafka
+On mac : 
+* ```boot2docker start ```
+* ```$(boot2docker shellinit)```
+* ```docker run -p 2181:2181 -p 9092:9092 --env ADVERTISED_HOST=`boot2docker ip` --env ADVERTISED_PORT=9092 spotify/kafka```
+* ```export ZOOKEEPER=`boot2docker ip`:2181```
+* ```export KAFKA=`boot2docker ip`:9092  ```
+* modify ./fixtures/integration.yml with values in $KAKFA and $ZOOKEEPER
+
+#### With JRuby
+
 * ```bundle exec jruby -S rspec spec/integration```
 
+#### With MRI
+
+* ```bundle install```
+* ```rake default``` or ```rake compile``` and then ```rake spec```
+* ```rake spec:intregration```
+