Add a complete code example for loading a model

[rangsimanketkaew]

I added a complete code example that can be used to confirm if the TensorFlow C++ API (built from source code with bazel) works.

[rangsimanketkaew]

@MarkDaoust I have my own repo for simply coding TF: https://github.com/rangsimanketkaew/tensorflow_cpp_api/blob/main/load_model_tensorflow_cpp.md. I can also help write a notebook for in-depth working with TF Ops, Graph, ClientSession, and etc. via C++ API.

There you can also find instructions for both saving and loading a model. This might be helpful for the users to get started as the documentation on the official TF website lacks a gentle introduction to and tutorial of the C++ API.

Let me know if you need anything else.