build-commit-from: Make docs match reality
build-commit-from: Make docs match reality

Move the -s short option from --src-repo to --subject,
as the docs say. This makes more sense, to go with -b
for --body.

Closes: #2527
Approved by: mwleeds

flatpak/flatpak,flatpak/flatpak,matthiasclasen/flatpak,matthiasclasen/flatpak,matthiasclasen/flatpak,flatpak/flatpak,matthiasclasen/flatpak,flatpak/flatpak,flatpak/flatpak,matthiasclasen/flatpak