fixed one last error

modules/ximgproc/include/opencv2/ximgproc/estimated_covariance.hpp

@@ -63,6 +63,7 @@ namespace ximgproc
 window forumlation.
 
 @param src The source image. Input image must be of a complex type.
+@param dst The destination estimated covariance matrix. Output matrix will be size (windowRows*windowCols, windowRows*windowCols) 
 @param windowRows The number of rows in the window.
 @param windowCols The number of cols in the window.
 The window size parameters control the accuracy of the estimation.