Add discussion of doctesting interactive code examples.

There have been various discussions about doctesting interactive code examples in the python docs. The consensus has been that it is desirable that they pass. Indeed, CI currently has a (pass-not-required) Tests / Docs / Doctest. (But it seems to be setup to be excessively lenient, passing many errors that are normally caught. Intended? Bug?) There has been additional discussion about use of particular features, such as doctest directives. An example from the doc:

The [ELLIPSIS](https://docs.python.org/3/library/doctest.html#doctest.ELLIPSIS) directive
gives a nice approach for the last example:
>>> C()  # doctest: +ELLIPSIS
<C object at 0x...>

Other people may remember such discussions better. In any case, a summary of current policy should be added either in
Documentation / Style Guide /Code Examples or in a new "Interactive Code Examples and Doctest" section immediately after.

阅读 Documentation/Style Guide/Code Examples 和 doctest 文档，尤其是交互式示例和指令指南。查看 Docs/Doctest CI 检查以及所引用的讨论，以确定当前策略，然后在现有章节中或紧接其后的新章节中添加简洁的总结。完成的标准是指南解释交互式示例所需的 doctest 行为以及相关指令。