docs: update android offline config (#251)

Author: JauneQ

docs/guides/solution/offlinePush.mdx

@@ -44,4 +44,5 @@ enable: #选择 getui 或者 fcm
 - [OpenIM Flutter Demo 配置说明](https://github.com/openimsdk/openim-flutter-demo/blob/main/CONFIGKEY.zh-CN.md)
 - [OpenIM iOS Demo 配置说明](https://github.com/openimsdk/openim-ios-demo/blob/main/CONFIGKEY.zh-CN.md)
 - [OpenIM Uniapp Demo 配置说明](https://github.com/openimsdk/open-im-uniapp-demo/blob/main/CONFIGKEY.md)
+- [OpenIM Android Demo 配置说明](https://github.com/openimsdk/open-im-android-demo/blob/main/CONFIGKEY.zh-CN.md)