docs: add diagrams for jj new -A and -B

[neongreen]

Checklist

If applicable:

• I have updated CHANGELOG.md
• I have updated the documentation (README.md, docs/, demos/)
• I have updated the config schema (cli/src/config-schema.json)
• I have added tests to cover my changes

[neongreen]

[neongreen]

I realize now that jj prev and jj parallelize show graphs vertically and not horizontally, but also I think horizontal graphs look nicer (the real argument) and save space in the CLI output (the objective argument).

I don't mind converting horizontal->vertical or vice versa, but I also don't mind leaving them in an inconsistent state and seeing which will eventually win.

[yuja]

Can you rewrite the graph without using non-ASCII characters? Unicode drawings might be rendered badly. I don't have any preference over horizontal/vertical.

[PhilipMetzger]

I agree with Yuya and think that the graph should be kept vertical to fit into the rest of the documentation as consistency is key.

[martinvonz]

I agree with Philip that the graphs should be consistent with our existing graphs to make it easier for users to read them.

I don't have much opinion between horizontal vs vertical per se (maybe a slight preference for vertical since it matches jj log). I care more about the consistency.

[neongreen]

I removed unicode and transmuted the diagrams

[PhilipMetzger]

last concistency nit from me, use the letters instead of numbers in the graph

[neongreen]

last concistency nit from me, use the letters instead of numbers in the graph

done, and I switched to --after and --before because -A A isn't great

[neongreen]

Hmmm. Anything I need to do to start the CI? Or is it just that the merge queue is long?

[emilazy]

You need to rebase this, it’s from before the CI changes so the mandatory job is never going to happen.