docs(angular): add reason for syncing

Author: thetaPC

docs/angular/testing.md

@@ -4,7 +4,7 @@ Ionic Framework supports multiple versions of Angular. As a result, we need to v
 
 ## Syncing Local Changes
 
-The Angular test app supports syncing your locally built changes for validation.
+The Angular test app supports syncing your locally built changes for validation. This allows you to test local changes like `core` without having to publish a new version of the package.
 
 1. Build the `core` directory.
 2. Navigate to `packages/angular` and run `npm run sync`.
@@ -16,6 +16,12 @@ The Angular test app supports syncing your locally built changes for validation.
 
 From here you can either build the application or start a local dev server. When re-syncing changes, you will need to [wipe or disable the application cache](#application-cache).
 
+> [!NOTE]
+> Syncing is required to verify that the minimal supported Angular version is still compatible with the latest Ionic Framework changes.
+> For example, Ionic Framework 8 supports Angular 16, but the latest version of Ionic Framework may not be compatible with Angular 16. Syncing allows you to verify that the latest changes are still compatible with the minimal supported version.
+>
+> Support for the minimal version and maximum version can be found on the [Support page](https://ionicframework.com/docs/reference/support#ionic-angular) of the Ionic Framework documentation.
+
 ## Application Cache
 
 Angular CLI creates a cache of several files on disk by default in the `.angular` directory. This decreases the time taken to build the test application. However, the cache makes it difficult to quickly sync and check local changes of Ionic. As a result, the `.angular` cache is disabled by default in the test app projects.