[Feat][C++][Doc] Add examples and tutorials about how to use the C++ Reader/Writer

[lixueclaire]

Is your feature request related to a problem? Please describe.
The C++ Reader/Writer is the most fundamental tools in the library of GraphAr. Currently, there are not enough resources for beginners to learn about how to use the C++ Reader/Writer. Although we have provided unit tests and API reference, they are not intuitive.

Describe the solution you'd like
Add corresponding examples in this directory refer to the tests, and add some tutorials in the documentation.

Additional context
related to #168

[lixueclaire]

Add examples under this directory about how to use C++ reader/writer.
We can refer to the examples provided by Arrow/Parquet.
These four examples are required in the first step:

• low_level_reader_example.cc
• mid_level_reader_example.cc
• mid_level_writer_example.cc

Optionally, add high-level examples:

• high_level_reader_example.cc
• high_level_writer_example.cc

High-level examples are optional since they are already included in the examples of out-of-core graph algorithms like PageRank, BFS and CC.