Add "How to Contribute" section to README #16343
Description
Similar to: https://github.com/apache/parquet-mr#how-to-contribute
Reporter: Wes McKinney / @wesm
Assignee: Wes McKinney / @wesm
Related issues:
- Arrow 0.3 release (blocks)
Note: This issue was originally created as ARROW-724. Please see the migration documentation for further details.