[in_app_purchase_android] Readme update for Alternative billing (#6578)

- **Add readme info about user choice billing and alternative billing**

Fixes flutter/flutter/issues/144992

Author: reidbaker

packages/in_app_purchase/in_app_purchase_android/CHANGELOG.md

@@ -1,6 +1,10 @@
+## 0.3.4+1
+
+* Adds documentation for UserChoice and Alternative Billing.
+
 ## 0.3.4
 
-* Adds `countryCode` API. 
+* Adds `countryCode` API.
 
 ## 0.3.3+1
 

packages/in_app_purchase/in_app_purchase_android/README.md

@@ -11,6 +11,14 @@ so you do not need to add it to your `pubspec.yaml`.
 However, if you `import` this package to use any of its APIs directly, you
 should [add it to your `pubspec.yaml` as usual][3].
 
+## Alternative/UserChoice Billing
+
+Alternative and UserChoice billing from Google Play is exposed from this package.
+
+Using the Alternative billing only feature requires Google Play app configuration, checking if the feature is available (`isAlternativeBillingOnlyAvailable`) and informing users that Google Play does not handle all aspects of purchase (`showAlternativeBillingOnlyInformationDialog`). After those calls then you can call `setBillingChoice` and respond when a user attempts a purchase.
+
+[Google Play documentation for Alternative billing](https://developer.android.com/google/play/billing/alternative)
+
 ## Migrating to 0.3.0
 To migrate to version 0.3.0 from 0.2.x, have a look at the [migration guide](migration_guide.md).
 

packages/in_app_purchase/in_app_purchase_android/pubspec.yaml

@@ -2,8 +2,7 @@ name: in_app_purchase_android
 description: An implementation for the Android platform of the Flutter `in_app_purchase` plugin. This uses the Android BillingClient APIs.
 repository: https://github.com/flutter/packages/tree/main/packages/in_app_purchase/in_app_purchase_android
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+in_app_purchase%22
-
-version: 0.3.4
+version: 0.3.4+1
 
 environment:
   sdk: ^3.1.0