Update Installation for ROS 2

The installation for ROS 2 in the [README](https://github.com/ros2-java/ros2_java/blob/main/README.md?plain=1#L47) is incorrect as it redirects to ROS index [causing issues](https://github.com/ros-infrastructure/rosindex/issues/385). It should be updated to what ever the latest branch is, or the rolling branch like so:
https://docs.ros.org/en/rolling/Installation.html