CopperheadOS on Android Verified Boot 2.0 docs

Documentation on using AVB (Android Verified Boot 2.0) on the Pixel 2 landed with some modifications:https://t.co/RBTcHinewfhttps://t.co/oFO4dnxhJ1

No longer need to find the flash handler for 'fastboot flash avb_custom_key' in the bootloader disassembly to make use of it…

— CopperheadOS (@CopperheadOS) January 12, 2018

Here's the pull request documenting it to make this far easier to the next person trying to figure it out: https://t.co/9O3dD93vtk.

— CopperheadOS (@CopperheadOS) January 6, 2018