docs: add next version badge to README and update blog install instructions

Author: hyochan

README.md

@@ -4,6 +4,7 @@
   <img src="https://hyochan.github.io/react-native-iap/img/icon.png" alt="React Native IAP Logo" width="150" />
 
 [![Version](http://img.shields.io/npm/v/react-native-iap.svg?style=flat-square)](https://npmjs.org/package/react-native-iap)
+[![Next Version](https://img.shields.io/npm/v/react-native-iap/next.svg?style=flat-square&label=next)](https://npmjs.org/package/react-native-iap)
 [![Download](http://img.shields.io/npm/dm/react-native-iap.svg?style=flat-square)](https://npmjs.org/package/react-native-iap)
 [![Backers and Sponsors](https://img.shields.io/opencollective/all/react-native-iap.svg)](https://opencollective.com/react-native-iap)
 [![CI - Test](https://github.com/hyochan/react-native-iap/actions/workflows/ci-test.yml/badge.svg)](https://github.com/hyochan/react-native-iap/actions/workflows/ci-test.yml)

docs/blog/2025-12-11-release-14.6.0-billing-programs.md

@@ -281,7 +281,7 @@ yarn add react-native-iap@next react-native-nitro-modules
 bun add react-native-iap@next react-native-nitro-modules
 ```
 
-This version is available via `npm install react-native-iap@next`. Check out the [documentation](/docs/next/intro) for details on all features.
+This version is available via `npm install react-native-iap@next react-native-nitro-modules`. Check out the [documentation](/docs/next/intro) for details on all features.
 
 ## References