Added information about highlighting python console examples in doc.

[bmispelon]

Trac ticket number

N/A

Branch description

I got confused by what the pycon language was in code examples and couldn't find an explanation in our docs. After figuring out it's used for interactive python console examples, I figured I'd mention it somewhere in the contributing docs.

Checklist

• This PR targets the main branch.
• The commit message is written in past tense, mentions the ticket number, and ends with a period.
• N/A I have checked the "Has patch" ticket flag in the Trac system.
• N/A I have added or updated relevant tests.
• I have added or updated relevant docs, including release notes if applicable.
• N/A I have attached screenshots in both light and dark modes for any UI changes.

[bmispelon]

If/once pygments/pygments#2697 is merged I would like to propose we switch to a less confusing name for this type of syntax highlighting.