some improvements on tutorials

modules/core/include/opencv2/core.hpp

@@ -273,6 +273,9 @@ of p and len.
 */
 CV_EXPORTS_W int borderInterpolate(int p, int len, int borderType);
 
+/** @example copyMakeBorder_demo.cpp
+An example using copyMakeBorder function
+ */
 /** @brief Forms a border around an image.
 
 The function copies the source image into the middle of the destination image. The areas to the
@@ -471,6 +474,9 @@ The function can also be emulated with a matrix expression, for example:
 */
 CV_EXPORTS_W void scaleAdd(InputArray src1, double alpha, InputArray src2, OutputArray dst);
 
+/** @example AddingImagesTrackbar.cpp
+
+ */
 /** @brief Calculates the weighted sum of two arrays.
 
 The function addWeighted calculates the weighted sum of two arrays as follows: