Diff explainer

The diff already shows what changed. What it can't show is why — why this approach and not the obvious one, what broke when you tried that, what you're nervous about, what you decided not to do. Supply that. Your reader is a sharp, time-poor developer who may not know this stack.

1. Work out what you're explaining

No argument means the current branch against its base, diffed from the merge base so other people's commits don't leak in.