更新文档中 `targetAccount` 与 `methodAccount` 的增减账户关系映射表

[ramsayleung]

Description

更新文档中 targetAccount 与 methodAccount 的增减账户关系映射表,

从逻辑上讲, defaultCashAccount 和 targetAccount 是由用户配置的值，是属于变量; 而 plusAccount和 minusAccount 属于每笔交易的固有属性, 因此将固有属性 plusAccount 和 minusAccount 作为表头, 变量作为随「收/支」而变化的值会让逻辑更清晰

Motivation and Context

https://github.com/deb-sig/double-entry-generator/discussions/103

Dependencies

None

Type of change

Please delete options that are not relevant.

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [x] This change requires a documentation update

How has this been tested?

1. All CI task passed
2. 账户的对应关系逻辑上保持一致

Is this change properly documented?

YES

Don't forget to add an entry to the CHANGELOG/README if necessary (new features, breaking changes, relevant internal improvements).

[gaocegege]

LGTM

Thanks for your contribution! :tada: :+1: