put some emphasis on choosing an image and support flashing any 4M image
externally.

This may help in refurbishing an x230 laptop.

the update function already uses it

upgrade.sh is gone

All we do is the bios vendor/version check. We can do that in any case.
Requirements don't change.

This patch adds two new payloads (memtestx86 and coreinfo)
to resolve #74.

thanks @alex-kazda

Fixes #85

This should fix #82

this actually got lost during updates for the release.

This feels like the last piece of the puzzle in chip-detection.

Fixes #82

me_cleaner says:
remove the ME/TXE Read/Write permissions to the other regions on the
flash from the Intel Flash Descriptor (requires a full dump).

Which sounds reasonable to do.

Fixes #76

For creating USB bios images from Lenovo's BIOS, we shouldn't duplicate
instructions. Things might change and break for users that way.

see #77

This makes things easier to maintain and simply causes less confusion
for users. We only want the lastest EC firmware.

Closes #77

While I think I have initially used 128 from some libreboot docs and never
had problems with it, I don't really see anybody use less than 512 right
now.

We recently added that the whole 8M chip flashing is optional, which is
important indeed. In brough some more stuff in which may be confusion.

We don't want to mention one specific OS because we're really generic
people should try to install whatever they want.

Also, "the command defaults to..." is misleading, as there are commandline
options applied in our example. Remove that.

And lastly, as long as users make the backups we always suggest in the
examples, they can change things at any time.

Despite I've never had any problems, applying external voltage to the
flash is considered dangerous, see #49 and #68. So change our documentation to
suggest not to do this often. Also, remove the note about "WoL power"
not being necessary. We don't document that (yet) anyways.

Fixes #68