Add the AndroidX stuff to the changelog

See libgdx/libgdx#7478.

_posts/2024/2024-10-17-gdx-1-13.md

@@ -29,6 +29,7 @@ The following changes require you to adapt your existing libGDX codebases:
 
 - [ANDROID] The minimum API level is now `19` (Android 4.4).
 - [ANDROID] Removed `Input#setCatchBackKey`, `#isCatchBackKey`, `#setCatchMenuKey`, and `#isCatchMenuKey` deprecated in 1.9.10. Use `#setCatchKey` and `#isCatchKey` instead.
+- [ANDROID] The Android backend now depends on AndroidX. To update your old projects, add `android.useAndroidX=true` to your `gradle.properties` file and add `implementation "androidx.core:core:1.13.1"` as dependency to your Android module.
 - [ANDROID & iOS] Exceptions occurring in `Runnable` tasks scheduled through `Gdx.app.postRunnable(...)` are no longer swallowed and will crash the app. Add a protection to your tasks if required.
 - [GWT] Updated to [GWT 2.11.0](https://www.gwtproject.org/release-notes.html#Release_Notes_2_11_0) from 2.10.0. This improves the JRE emulation to support features from Java 11 like collections, streams, and more. To keep old projects working, add `com.google.jsinterop:jsinterop-annotations:2.0.2:sources` as dependency to your html subproject.
 - [iOS] The minimum supported iOS version is now 12.0. Update your `Info.plist` file if necessary.