message: Update cmake document for Android build
diff: @@ -40,11 +40,39 @@ cd tflite_build
  cmake ../tensorflow_src/tensorflow/lite
  ```
  +If you want to configure Android build with GPU delegate support,
  +
  +```sh
  +mkdir tflite_build
  +cd tflite_build
  +cmake -DCMAKE_TOOLCHAIN_FILE=<NDK path>/build/cmake/android.toolchain.cmake \
  + -DANDROID_ABI=arm64-v8a -DTFLITE_ENABLE_GPU=ON ../tensorflow_src/tensorflow/lite
  +```
  +
  +
  #### Step 4. Build TensorFlow Lite
  +In the tflite_build directory,
  +
  ```sh
  cmake --build . -j
  ```
  +Or
  +
  +```sh
  +make -j
  +```
  +
  +
  **Note:** This should compile a static library `libtensorflow-lite.a` in the
  current directory.
  +
  +
  +#### Step 5. Build TensorFlow Lite Benchmark Tool
  +
  +In the tflite_build directory,
  +
  +```sh
  +make benchmark_model -j
  +```
  