Updated readme with launch file calls and link references

Author: andreucm

README.md

@@ -1,2 +1,18 @@
 # usb_cam_calibration
-Calibration of an usb camera using usb_cam and camera_calibration ROS packages
+Calibration of an usb camera using [usb_cam](http://wiki.ros.org/usb_cam) and [camera_calibration](http://wiki.ros.org/camera_calibration) ROS packages
+
+### To calibrate a camera
+```shell
+$ roslaunch usb_cam_calibration usb_camera_calibration.launch video_device:="/dev/video1"
+```
+
+### To see raw and rectified images after calibration
+```shell
+$ roslaunch usb_cam_calibration usb_camera_calibrated.launch video_device:="/dev/video1"
+```
+
+### Tutorial and references
+- http://wiki.ros.org/camera_calibration/Tutorials/MonocularCalibration
+- https://docs.opencv.org/2.4/doc/tutorials/calib3d/camera_calibration/camera_calibration.html
+- https://docs.opencv.org/2.4/_downloads/pattern.png
+