DQT - distance description documentation

-Added description of distance calculation in the readme file
-Updated destination explanation in DQT

Tracked on: DSO-8086

tools/depth-quality/depth-quality-model.cpp

@@ -617,7 +617,7 @@ namespace rs2
                         ImGui::Text("Distance:");
                         if (ImGui::IsItemHovered())
                         {
-                            ImGui::SetTooltip("Estimated distance to the wall in mm");
+                            ImGui::SetTooltip("Estimated distance to an average within the ROI of the target (wall) in mm");
                         }
                         ImGui::SameLine(); ImGui::SetCursorPosX(col1);
                         ImGui::Text("%.2f mm", _metrics_model.get_last_metrics().distance);

tools/depth-quality/readme.md

@@ -38,6 +38,13 @@ You should be able to easily get and interpret several of the depth quality metr
 ### Fill Rate
 the percentage of valid (non-zero) pixels within the user-defined Region of Interest (ROI) area.
 
+### Distance To Target
+estimated distance to an average within the ROI of the target (wall) in mm.  
+_N_ - Normal of the fitted plane  
+_P_ - Center of ROI(centroid)  
+
+![](./res/distance.gif)
+
 ### Plane Fit RMS Error
 the metrics represents depth pixels deviation from the calculated Plane Fit.
 _Dist<sub>i</sub>_ - Distance from depth pixel coordinates to the Plane Fit (mm).