docs(upgrade): add guide about downgradeModule() (#18487)

PR Close #18487

packages/upgrade/src/static/downgrade_module.ts

@@ -18,8 +18,6 @@ import {NgAdapterInjector} from './util';
 
 
 /**
- * <!-- TODO(gkalpak): Add link to guide. -->
- *
  * @description
  *
  * A helper function for creating an AngularJS module that can bootstrap an Angular module
@@ -49,6 +47,9 @@ import {NgAdapterInjector} from './util';
  *
  * {@example upgrade/static/ts/lite/module.ts region="basic-how-to"}
  *
+ * For more details on how to use `downgradeModule()` see
+ * [Upgrading for Performance](guide/upgrade-lite).
+ *
  * @usageNotes
  *
  * Apart from `UpgradeModule`, you can use the rest of the `upgrade/static` helpers as usual to
@@ -84,6 +85,9 @@ import {NgAdapterInjector} from './util';
  * especially in change-detection-heavy applications, but leaves it up to the developer to manually
  * notify each framework as needed.
  *
+ * For a more detailed discussion of the differences and their implications, see
+ * [Upgrading for Performance](guide/upgrade-lite).
+ *
  * <div class="alert is-helpful">
  *
  *   You can manually trigger a change detection run in AngularJS using