Thats just usefull if you want to install it from source and will also work ( probably when you got no sudo rights). I'm not quite sure but the package should be awailable if you install ROS with sudo apt-get install ros-indigo-desktop-full. Otherwise you can install it with sudo apt-get install ros-indigo-vision-opencv. For using OpenCV at your ROS nodes please follow the tutorials at cv_bridge Tutorials.