Add xmldoc for updateBindTarget

osu.Game/Overlays/KeyBinding/KeyBindingRow.cs

@@ -320,6 +320,9 @@ protected override void OnFocusLost(FocusLostEvent e)
             base.OnFocusLost(e);
         }
 
+        /// <summary>
+        /// Updates the bind target to the currently hovered key button or the first if clicked anywhere else.
+        /// </summary>
         private void updateBindTarget()
         {
             if (bindTarget != null) bindTarget.IsBinding = false;