PARQUET-2479: Update README with link to parquet website, clarify contents

[alamb]

https://issues.apache.org/jira/browse/PARQUET-2479

As part of clarifying and improving the public communication about Parquet, I think we should also link parquet-format to the parquet.apache.org website

Also, the text in the format repo's readme is somewhat unclear on what is in the repo and how it related to other projects, so I clarified that as well

You can see the rendered version of the README here: https://github.com/alamb/parquet-format/tree/alamb/doc_link_readme?tab=readme-ov-file#parquet-

Jira

• [x] My PR addresses the following Parquet Jira issues and references them in the PR title. For example, "PARQUET-1234: My Parquet PR"
  • https://issues.apache.org/jira/browse/PARQUET-2479
  • In case you are adding a dependency, check if the license complies with the ASF 3rd Party License Policy.

Commits

• [x] My commits all reference Jira issues in their subject lines. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters (not including Jira issue reference)
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

Documentation

This is a README only change

• [x] In case of new functionality, my PR adds documentation that describes how to use it.
  • All the public functions and the classes in the PR contain Javadoc that explain what it does

[alamb]

Thank you for the review @wgtmac and @vinooganesh