Follow up improvements to verification guide for `parquet-java` release

Follow up to https://github.com/apache/parquet-site/pull/98

> We can also take some inspiration from https://iceberg.apache.org/how-to-release/#how-to-verify-a-release

_Originally posted by @kevinjqliu in https://github.com/apache/parquet-site/pull/98#pullrequestreview-4757651125_
            