Update doc/tutorials/core/adding_images/adding_images.rst
Update doc/tutorials/core/adding_images/adding_images.rst

Quick fix for: http://code.opencv.org/issues/2803
opencv/opencv,apavlenko/opencv,opencv/opencv,apavlenko/opencv,apavlenko/opencv,opencv/opencv,opencv/opencv,opencv/opencv,apavlenko/opencv,opencv/opencv,opencv/opencv,apavlenko/opencv,apavlenko/opencv,opencv/opencv,opencv/opencv,opencv/opencv