Add link to parquet.apache.org in parquet-mr repo

[asfimport]

https://github.com/apache/parquet-mr does not link to the parquet.apache.org website.

 

I think the content is also somewhat confusing as it talks about parquet being part of hadoop ecosystem when its role is clearly broader at this point

 

It would be nice to clarify the readme 

Reporter: Andrew Lamb / @alamb Assignee: Andrew Lamb / @alamb

PRs and other links:

• GitHub Pull Request #1355
• GitHub Pull Request #1355

_{Note: This issue was originally created as PARQUET-2478. Please see the migration documentation for further details.}