flashing recovery:
1. Reboot to bootloader
2. fastboot flash boot boot.img
3. fastboot flash vendor_boot vendor_boot.img
4. fastboot reboot recovery
flashing ROM:
1. Apply Update --> from ADB
2. adb sideload rom.zip
3. Format Data
4. reboot to recovery (again)
5. Install any gapps or packages
6. reboot to system