Improve the xdg-app-builder man page
Improve the xdg-app-builder man page

Fix some inconsistencies, and update the example to not
not use app-id.

alexlarsson/xdg-app,alexlarsson/xdg-app,flatpak/flatpak,flatpak/flatpak,alexlarsson/xdg-app,matthiasclasen/flatpak,GeorgesStavracas/flatpak,flatpak/flatpak,flatpak/flatpak,handsome-feng/flatpak,matthiasclasen/flatpak,matthiasclasen/flatpak,matthiasclasen/xdg-app,flatpak/flatpak,handsome-feng/flatpak,amigadave/flatpak,matthiasclasen/xdg-app,handsome-feng/flatpak,handsome-feng/flatpak,handsome-feng/flatpak,GeorgesStavracas/flatpak,GeorgesStavracas/flatpak,matthiasclasen/flatpak,alexlarsson/xdg-app,GeorgesStavracas/flatpak,matthiasclasen/xdg-app,amigadave/flatpak,matthiasclasen/xdg-app,GeorgesStavracas/flatpak,matthiasclasen/flatpak,amigadave/flatpak,amigadave/flatpak