Add vendor flash instructions for bullhead (Nexus 5X)
On first install on a Nexus 5X, i was greated by a "Vendor mismatch" and "ui stopped" alerts. Solving this require flashing the right vendor version. This should be added to the documentation.
Basically, all there is to do is rebooting into bootloader and flash with
fastboot flash vendor vendor-bullhead-opm7.181205.001.img