docs: build information for Android

frontends/libretro/README.md

@@ -5,3 +5,30 @@
 ```bash
 cargo build
 ```
+
+### Android
+
+Configure `NDK_HOME` environment variable to point to your Android NDK directory and then create local toolchain replicas in the root project directory using:
+
+```bash
+mkdir -p ndk
+${NDK_HOME}/build/tools/make_standalone_toolchain.py --api 26 --arch arm64 --install-dir ndk/arm64
+${NDK_HOME}/build/tools/make_standalone_toolchain.py --api 26 --arch arm --install-dir ndk/arm
+${NDK_HOME}/build/tools/make_standalone_toolchain.py --api 26 --arch x86 --install-dir ndk/x86
+```
+
+To install the Rust targets for Android using rustup run:
+
+```bash
+rustup target add aarch64-linux-android
+rustup target add armv7-linux-androideabi
+rustup target add i686-linux-android
+```
+
+Then you're ready to build Boytacean's libretro core using the following commands (for release builds):
+
+```bash
+cargo build --target=aarch64-linux-android --release
+cargo build --target=armv7-linux-androideabi --release
+cargo build --target=i686-linux-android --release
+```