message: Update README.md of TFLite benchmark tool for Flex delegate
  Add an example of using benchmark_model_plus_flex target
diff: @@ -297,3 +297,28 @@ some additional parameters as detailed below.
  * `random_shuffle_benchmark_runs`: `bool` (default=true) \
  Whether to perform all benchmark runs, each of which has different
  performance options, in a random order.
  +
  +## Build the benchmark tool with Tensorflow ops support
  +
  +You can build the benchmark tool with [Tensorflow operators support](https://www.tensorflow.org/lite/guide/ops_select).
  +
  +### How to build
  +
  +To build the tool, you need to use 'benchmark_model_plus_flex' target with
  +'--config=monolithic' option.
  +
  +```
  +bazel build -c opt \
  + --config=monolithic \
  + tensorflow/lite/tools/benchmark:benchmark_model_plus_flex
  +```
  +
  +### How to benchmark tflite model with Tensorflow ops
  +
  +Tensorflow ops support just works the benchmark tool is built with Tensorflow
  +ops support. It doesn't require any additional option to use it.
  +
  +```
  +bazel-bin/tensorflow/lite/tools/benchmark/benchmark_model_plus_flex \
  + --graph=model_converted_with_TF_ops.tflite \
  +```
  