docs: mark the entryComponents array as deprecated (#38616)

The `entryComponents` array is now deprecated (per https://angular.io/api/core/NgModule#entryComponents
and https://angular.io/guide/deprecations#entryComponents).

PR Close #38616

aio/content/guide/entry-components.md

@@ -76,6 +76,12 @@ All router components must be entry components. Because this would require you t
 
 ## The `entryComponents` array
 
+<div class="alert is-helpful">
+
+Since 9.0.0 with Ivy, the `entryComponents` property is no longer necessary. See [deprecations guide](guide/deprecations#entryComponents).
+
+</div>
+
 Though the `@NgModule` decorator has an `entryComponents` array, most of the time
 you won't have to explicitly set any entry components because Angular adds components listed in `@NgModule.bootstrap` and those in route definitions to entry components automatically. Though these two mechanisms account for most entry components, if your app happens to bootstrap or dynamically load a component by type imperatively,
 you must add it to `entryComponents` explicitly.