gh-132661: docs: add a t-string tutorial

[davepeck]

During the first pass at t-string docs, we wrote a potential addition to the Fancier Output Formatting section of the Input/Output Tutorial.

It didn't quite feel ready, and maybe wasn't in the right corner of the docs, so we decided to break it out into a separate PR and wrestle it to its final form. :-)

CC @encukou and @AA-Turner -- happy to drop this entirely, or massage it into something better.

See also Trey's useful comments on the tutorial.

• Issue: Implement PEP 750 – Template Strings #132661

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📚 Documentation preview 📚: https://cpython-previews--137213.org.readthedocs.build/

[davepeck]

(Marking as ready so we get some eyes on this. I think there are a lot of directions we can take this content, including simply deciding not to include it in the Python docs whatsoever. Hopefully there's something useful here, though?)

[AA-Turner]

I'll add this to my to-do list. I have a few reorganisation thoughts after a quick skim, but I want to look at things properly before doing so. Would you mind if I push directly to the branch? GH makes it hard to effectively suggest that kind of change.

A

[davepeck]

Would you mind if I push directly to the branch?

Not at all; please do! The more eyes and authors the better here, I think.