MINOR: updated document of parquet-avro (#2914)

I have added major aspects of `Apache parquet-avro` ,
Parquet-Avro integration,
Specific and practical applications of apache parquet avro,
Parquet-avro API overview
Writing avro data to parquet files
Reading avro data from parquet files
Converting avro schemas to parquet schemas
Additional API classes and methods

No file, test, or entry point is named. Locate the existing parquet-avro documentation and compare it with the listed topics, including integration, API usage, reading and writing data, and schema conversion. Done means the requested coverage is present and the documentation builds or renders successfully.

Written by the indexing model from the issue text.