Consolidate guidance on prompts in interactive code examples

In the Documentation chapter, Style Guide / Code Examples has

The ellipsis for the sys.ps2 secondary interpreter prompt should only be used sparingly, where it is necessary to clearly differentiate between input lines and output lines. Besides contributing visual clutter, it makes it difficult for readers to cut-and-paste examples so they can experiment with variations.

(Perhaps it should be mentioned here that doctesting the code example requires such differentiation and hence requires secondary prompts. Perhaps the primary prompt should also be left off.)

reStructured Text Markup / Additional Markup Constructs / Showing Code Examples has

Representing an interactive session requires including the prompts and output along with the Python code. No special markup is required for interactive sessions. After the last line of input or output presented, there should not be an “unused” primary prompt; this is an example of what not to do:

>>>1 + 1
2
>>>

I think both advices should be in the same place and a reference added in the other.

Open the linked Style Guide / Code Examples and reStructured Text Markup / Showing Code Examples sections first. Consolidate their guidance on interactive prompts in one place, add a reference in the other, and ensure the resulting advice covers secondary prompts, doctesting, and the unused primary prompt example.