added some documentation

README.md

 # rosjava_gradle
 
+## How to start it
+
+* Import into IntelliJ as Gradle Project
+* Run it via right klicking the main class and by hitting the play button
+
+## Code Sources
+
+* Where can I find important imports? -> https://github.com/rosjava/android_core
+* This code is based on an analysis of rosjavas android code
+    * http://docs.ros.org/en/hydro/api/android_apps/html/Listener_8java_source.html
+    * http://wiki.ros.org/rosjava/Tutorials/Create%20a%20ROS%20Android%20Node
+    * https://github.com/rosjava/android_core/tree/kinetic/android_tutorial_pubsub