Document difference between Vector and VectorImage layers

src/ol/layer/Vector.js

@@ -6,7 +6,11 @@ import CanvasVectorLayerRenderer from '../renderer/canvas/VectorLayer.js';
 
 /**
  * @classdesc
- * Vector data that is rendered client-side.
+ * Vector data is rendered client-side, as vectors. This layer type provides most accurate rendering
+ * even during animations. Points and labels stay upright on rotated views. For very large
+ * amounts of vector data, performance may suffer during pan and zoom animations. In this case,
+ * try {@link module:ol/layer/VectorImage~VectorImageLayer}.
+ *
  * Note that any property set in the options is set as a {@link module:ol/Object~BaseObject}
  * property on the layer object; for example, setting `title: 'My Title'` in the
  * options means that `title` is observable, and has get/set accessors.