Add instruction to re-compile the code

modules/tracking/doc/diagrams.markdown

@@ -237,7 +237,7 @@ MultiTracker diagram
 @enduml
 
 @startuml{multi_tracker_uml.png}
-  package "MultiTracker package" #DDDDDD {
+  package "MultiTracker class" #DDDDDD {
 
   class MultiTracker{
     MultiTracker(const String& trackerType = "" );

modules/tracking/samples/multitracker.cpp

@@ -11,7 +11,11 @@
  * to enable the high precission of fps computation
  *--------------------------------------------------*/
 
-#define HAVE_OPENCV
+/* after the OpenCV libary is installed
+ * please uncomment the the line below and re-compile this code
+ * to enable high precission of fps computation
+ */
+//#define HAVE_OPENCV
 
 #include <opencv2/core/utility.hpp>
 #include <opencv2/tracking.hpp>