docs: add AOT mode default to version 9 upgrade doc (#33703)

PR Close #33703

aio/content/guide/ivy-compatibility.md

@@ -11,7 +11,7 @@ That said, some applications will likely need to apply some manual updates.
 In version 9, [a few deprecated APIs have been removed](guide/updating-to-version-9#removals) and there are a [few breaking changes](guide/updating-to-version-9#breaking-changes) unrelated to Ivy.
 If you're seeing errors after updating to version 9, you'll first want to rule those changes out.
 
-To do so, temporarily [turn off Ivy in your `tsconfig.json`](guide/ivy#opting-out-of-angular-ivy) and re-start your app.
+To do so, temporarily [turn off Ivy](guide/ivy#opting-out-of-angular-ivy) in your `tsconfig.json` and re-start your app.
 
 If you're still seeing the errors, they are not specific to Ivy. In this case, you may want to consult the [general version 9 guide](guide/updating-to-version-9).
 

aio/content/guide/updating-to-version-9.md

@@ -28,9 +28,14 @@ If you're curious about the specific migrations being run (e.g. what code is cha
 
 - Angular now compiles with Ivy by default. See [Ivy compatibility section](#ivy).
 
+- CLI apps compile in [AOT mode](/guide/aot-compiler) by default (which includes template type-checking). 
+Users who only built with JIT before may see new type errors. 
+See our [template type-checking guide](guide/template-typecheck) for more information and debugging tips.
+
 - Typescript 3.4 and 3.5 are no longer supported. Please update to Typescript 3.6.
 
-- tslib is now listed as a peer dependency rather than a direct dependency. Users not using the CLI will need to manually install tslib via `yarn add tslib` or `npm install tslib --save`.
+- tslib is now listed as a peer dependency rather than a direct dependency. 
+Users not using the CLI will need to manually install tslib via `yarn add tslib` or `npm install tslib --save`.
 
 {@a deprecations}
 ### New Deprecations