add comment advising against adding window listeners in tooltip manager

src/tooltip-manager.js

@@ -152,6 +152,7 @@ class TooltipManager {
       tooltip.hide()
     }
 
+    // note: adding a listener here adds a new listener for every tooltip element that's registered.  Adding unnecessary listeners is bad for performance.  It would be better to add/remove listeners when tooltips are actually created in the dom. 
     window.addEventListener('resize', hideTooltip)
 
     const disposable = new Disposable(() => {