Merge pull request #15 from hiking90/main

Add Android descriptions

src/android-build.md

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+# Android Build
+## NDK Install
+The NDK can be installed using Android Studio, or it can be downloaded and installed from the following URL.
+
+* [NDK guides](https://developer.android.com/ndk/guides)
+* [NDK downloads](https://developer.android.com/ndk/downloads)
+
+## Cargo NDK Install
+To build rsbinder using the NDK, the installation of [cargo-ndk](https://crates.io/crates/cargo-ndk) is required.
+
+## Build **rsbinder** with NDK
+After installing cargo-ndk, various targets were installed with ```$ rustup target add```. Use this target information to build with the following command.
+
+```
+$ cargo ndk -t x86_64-linux-android build
+```
+

src/android.md

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+**rsbinder** supports not only Linux but also Android. Since Android already has an environment prepared for binder communication, **rsbinder**, **rsbinder-aidl**, and **rsbinder-hub** are utilized for development. There is no need to create a binder device or run a service manager, so **rsbinder-tools** are not used.
+
+For building in the Android environment, it is necessary to install the NDK, and an additional Rust build environment that utilizes the NDK is required.
+
+[Android Build](./android-build.md)
+
+## Compatibility with Android Versions
+안드로이드 버전에 따른 Binder IPC에 대한 호환성 문제가 있다.
+현재 확인된 사항은 Android 12를 기준으로 그 이전, 이후의 호환성 문제가 있다.
+
+당신의 SW가 Android 11과 12에서 모두 동작해야 한다면, Android 버전을 rsbinder::set_android_version() api를 통해 설정해야 한다.
+
+Android Version 정보는 다음과 같이 확인하고, 설정할 수 있다.
+
+```
+use android_system_properties::AndroidSystemProperties;
+
+let properties = AndroidSystemProperties::new();
+
+if let Some(version) = properties.get("ro.build.version.release") {
+    rsbinder::set_android_version(version.parse())
+}
+```