add some info in README about joystick

src/platforms/ros/nodes/README.md

@@ -2,3 +2,21 @@
 
 This directory contains several small ROS nodes which are intended to run alongside the PX4 multi-platform nodes in
 ROS. They act as a bridge between the PX4 specific topics and the ROS topics.
+
+## Joystick Input
+
+You will need to install the ros joystick packages
+See http://wiki.ros.org/joy/Tutorials/ConfiguringALinuxJoystick
+
+### Arch Linux
+```sh
+yaourt -Sy ros-indigo-joystick-drivers --noconfirm
+```
+check joystick
+```sh
+ls /dev/input/
+ls -l /dev/input/js0
+```
+(replace 0 by the number you find with the first command)
+
+make sure the joystick is accessible by the `input` group and that your user is in the `input` group