add doxygen comment for X_coord, Y_coord, and layer_coord

Author: soheilshahrouz

vpr/src/place/move_generators/median_move_generator.h

@@ -66,7 +66,10 @@ class MedianMoveGenerator : public MoveGenerator {
                                              bool& skip_net);
 
   private:
+    /// Stores x positions to find the median
     std::vector<int> X_coord;
+    /// Stores y positions to find the median
     std::vector<int> Y_coord;
+    /// Stores layer positions to find the median
     std::vector<int> layer_coord;
 };

vpr/src/place/move_generators/weighted_median_move_generator.h

@@ -46,7 +46,10 @@ class WeightedMedianMoveGenerator : public MoveGenerator {
                                              t_bb_cost* coords);
 
   private:
+    /// Stores x positions to find the median
     std::vector<int> X_coord;
+    /// Stores y positions to find the median
     std::vector<int> Y_coord;
+    /// Stores layer positions to find the median
     std::vector<int> layer_coord;
 };