Tutorial create pattern grid for calibration using gen_pattern.py

doc/tutorials/calib3d/camera_calibration_pattern/camera_calibration_pattern.markdown

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+Create calibration pattern {#tutorial_camera_calibration_pattern}
+=========================================
+
+The goal of this tutorial is to learn how to create calibration pattern.
+
+You can find a chessboard pattern in https://github.com/opencv/opencv/blob/3.4/doc/pattern.png
+
+You can find a circleboard pattern in https://github.com/opencv/opencv/blob/3.4/doc/acircles_pattern.png
+
+Create your own pattern
+---------------
+
+Now, if you want to create your own pattern, you will need python to use https://github.com/opencv/opencv/blob/3.4/doc/pattern_tools/gen_pattern.py
+
+Example
+
+create a checkerboard pattern in file chessboard.svg with 9 rows, 6 columns and a square size of 20mm:
+
+        python gen_pattern.py -o chessboard.svg --rows 9 --columns 6 --type checkerboard --square_size 20
+
+create a circle board pattern in file circleboard.svg with 7 rows, 5 columns and a radius of 15mm:
+
+        python gen_pattern.py -o circleboard.svg --rows 7 --columns 5 --type circles --square_size 15
+
+create a circle board pattern in file acircleboard.svg with 7 rows, 5 columns and a square size of 10mm and less spacing between circle:
+
+        python gen_pattern.py -o acircleboard.svg --rows 7 --columns 5 --type acircles --square_size 10 --radius_rate 2
+
+If you want to change unit use -u option (mm inches, px, m)
+
+If you want to change page size use -w and -h options
+
+If you want to create a ChArUco board read tutorial Detection of ChArUco Corners in opencv_contrib tutorial(https://docs.opencv.org/3.4/df/d4a/tutorial_charuco_detection.html)