PEP 678: add post-history, minor tweaks following discussion

[Zac-HD]

Following the post on python-dev which requested comments to this Discuss thread, I've updated PEP 678 with Post-History and some minor clarifications following that discussion.

I believe that after this PR is merged, the PEP is ready for consideration by the Steering Council.

My deep thanks again to everyone who has helped me through this, especially the many thoughtful commenters, those who proof-read and contributed fixes, and to Irit for her support and sponsorship throughout 🙏

[iritkatriel]

Thank you Zac for your work on this PEP.

Once the discussion has been idle for a week or so, this indeed looks ready to be submitted to the SC (you do that by creating an issue on the SC tracker, such as this one python/steering-council#98).

[CAM-Gerlach]

Thanks. A couple small copyedits, and one general procedural comment.

Also, please add a link to the Discourse thread to the header between Sponsor and Status, as required by PEP 1 and PEP 12, and which makes it far more accessible for users coming across the PEP now or in the future to find. I.e.:

Discussions-To: https://discuss.python.org/t/13374

[CAM-Gerlach]

There's no formal requirement I can find in PEP-0001, but less than a week of discussion and review between announcing/opening a discussion thread for a PEP and submitting it for final consideration for the SC seems a little short, at least to me...

[AA-Turner]

Thanks @Zac-HD

Please could you line wrap to 79 per PEP 12 in a followup PR before submission to the Council.

A