message: Update the document for label_image.
diff: @@ -102,7 +102,7 @@ CMake project. Please refer the
  ["Create a CMake project which uses TensorFlow Lite"](#create_a_cmake_project_which_uses_tensorflow_lite)
  section.
  -### Step 6. Build TensorFlow Lite Benchmark Tool and Label Image Example
  +### Step 6. Build TensorFlow Lite Benchmark Tool and Label Image Example(Optional)
  In the tflite_build directory,
  