Make a button for copypasting setup commands

[KralaBenjamin]

I followed the setup page on https://flatpak.org/setup/Ubuntu and once I miscopied one line of command.

On other pages of flathub page you can copypaste the command (e.g. application page, https://flathub.org/apps/details/org.gnome.gitlab.somas.Apostrophe) It would be wonderful if you can do it also on the setup page.