we have reproducible builds and are (almost) done with ch341a support

shamelessly taken from https://github.com/Thrilleratplay/coreboot-builder-scripts

thanks a lot!

Fixes #31

To make a GRUB bootloader installation (on the HDD) work, the graphical
console has to be disabled in /etc/default/grub :

	GRUB_TERMINAL=console

Remember to apply the change using update-grub. The menu is displayed in
text mode.

This is also discussed in #4

Closes #24

This should de-duplicate and simplify our docs.

Fixes #27

Now our scripts start with _where_ it should be run. x230_*.sh should
be run on the x230 where Skulls should be installed. external_*.sh
obviously not.

This also adds the -f <flasher> option and an interactive menu if not
specified.