docs(select): add object comparison warning

Author: dmvt

src/ng/directive/select.js

@@ -19,6 +19,11 @@ var ngOptionsMinErr = minErr('ngOptions');
  * represented by the selected option will be bound to the model identified by the `ngModel`
  * directive.
  *
+ * <div class="alert alert-warning">
+ * **Note:** `ngModel` compares by reference, not value. This is important when binding to an
+ * array of objects. See an example {@link http://jsfiddle.net/qWzTb/ in this jsfiddle}.
+ * </div>
+ *
  * Optionally, a single hard-coded `<option>` element, with the value set to an empty string, can
  * be nested into the `<select>` element. This element will then represent the `null` or "not selected"
  * option. See example below for demonstration.