[Java] Provide guidance in documentation for using Arrow in an uberjar setting

Currently, ArrowBuf class directly access the package-private fields of AbstractByteBuf class which makes shading Apache Arrow problematic. If we relocate io.netty namespace excluding io.netty.buffer.ArrowBuf, it would throw out IllegalAccessException.

**Reporter**: [Jingyuan Wang](https://issues.apache.org/jira/browse/ARROW-799) / @alphalfalfa
#### Related issues:
- [[Java] Make Arrow library more shade-friendly](https://github.com/apache/arrow/issues/16325) (relates to)

_{**Note**: *This issue was originally created as [ARROW-799](https://issues.apache.org/jira/browse/ARROW-799). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

從 issue 中連結的遷移文件開始，檢視其中描述的 ArrowBuf 與 AbstractByteBuf shading 互動。記錄如何在 uberjar 中使用 Arrow，包括 io.netty 的 relocation 限制和 IllegalAccessException 情境；當使用者能清楚了解 workaround 時，即視為完成。

由索引模型根據 Issue 內容生成。