Update docs to indicate the need for firmware keys. Drop support for a9x.

[aihkas]

After struggling to get things to work for A9x, I was stuck because there are no publicly available firmware keys for the iPad pro first gen.
Is there any way or a guide on how to work on extracting the firmware keys? checkm8 should've made it possible AFAIK.

I also suggest adding a note about that in the readme or the guide. iPhone Wiki - Firmware Keys

Device found in DFU Mode.
Getting firmware keys for: j99aap
Cleaning up...
[exception]:
what=getting keys failed with error: 14745615 (failed to get FirmwareJson from Server). Are keys publicly available?
code=41549892

[aihkas]

Using gaster to decrypt iBSS seems to work. Gotta figure out how to pass it to futurerestore later.

[aihkas]

If anyone ends up in the same situation, I managed to decrypt and get the keys. Still gotta work on a workaround, so futurerestore grabs them locally in some way or another, maybe by tunneling the connection.

[aihkas]

Update: even after successfully passing the firmware keys, futurerestore will fail with ApNonce from device doesn't match IM4M nonce after applying ApNonce hax. Aborting! I suggest dropping support for a9x. (iPad6,8, s8001).
All the available methods will fail to set the apnonce for the iPad pro first gen because, technically, all methods to patch or remove the signature checks for this chip are flawed. gaster tool seems close to sorting it out, but it is still not perfect (It could be related to cache problems with the used methodology).

[aihkas]