Add initial documentation about flashing Libreboot on supported ChromeOS
devices. Link the Chromebooks in the hardware index to it. I only have
tried firmware work on gru-kevin, so there is an implicit focus on that,
but most others should be similar.
The one exception is gru-bob, as it is new enough to support Closed Case
Debugging which can be used to disable write-protect and flash the
firmware externally. Provide links to the ChromiumOS docs for that.
Although not supported on Libreboot, x86 Chromebooks still carry the
curse that is unreadable non-redistributable Intel ME firmware, so
provide a warning against flashing x86 images without it just in case.
Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>