Update README.md

mace/examples/android/README.md

 Android Demo
-------------
-------------
-
-Try it by downloading the [APK](https://cnbj1.fds.api.xiaomi.com/mace/demo/mace_android_demo.apk).
+=============
 
 How to build
 ---------------
-* Build native library, please refer to [docs](docs) for more information.
-    ```
-    # Execute following commands from the project's root directory
-    python tools/converter.py build --config=docs/getting_started/models/demo_app_models.yaml
-    cp -r build/mobilenet/include/ mace/examples/android/macelibrary/src/main/cpp/
-    cp -r build/mobilenet/lib/ mace/examples/android/macelibrary/src/main/cpp/
-    ```
-* Build APK
-  * Import the `mace/examples/android` directory as a new Android Studio project and select `install run`
-  * Or build it with gradle:
-    ```
-    cd mace/exampls/android
-    ./gradlew installAppRelease
-    ```
-* You can also build native library and APK with `mace/examples/android/build.sh`
-    ```
-    cd mace/exampls/android
-    ./build.sh
-    ```
+
+```sh
+cd mace/exampls/android
+./build.sh
+```
+
+Pre-built APK
+--------------
+Pre-built Android APK can be downloaded [here](https://cnbj1.fds.api.xiaomi.com/mace/demo/mace_android_demo.apk).
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