Move parquet-java specific contributing content to parquet-java

[alamb]

This came up as part of #190

There is parquet-java specific content on the overall parquet website. I think it would be more discoverable if it lived with the code / github flow for that other repo.

Thus I propose putting the details of contributing to parquet-java into a CONTRIBUTING.md or similar page in the parquet-java repo https://github.com/apache/parquet-java

Originally posted by @alamb in #190 (review)