you need to unlock your bootloader first, then flashboot TWRP126.96.36.199.0 first.
then reboot in recovery(TWRP) advance-and choose sideload. then flashboot-sideload your zip file, all is in the link you were given above.
Then report back if you need any more help
Set_metadata_recursive: some changes failed
E: Error executing updater binary in zip '/data/media/sideload.zip'
Any other ideas appreciated?