I've been pretty much following the steps within the scripts found in https://github.com/ubports/device-builds, and after some code adjustments have been able to build ubp-5.1-allthefixings on my ubuntu 18.04 box.
However, now that I have the device_hammerhead_devel.tar.xz file ready, I am not sure of the next steps... Unfortunately I do not have the ubuntu-device-flash as that package did not exist under 18.04.
Can anyone explain the next steps? Do I fastboot into recovery, copy the xz files and install (similar to lineageOS)? Do I need to use some other tool to flash my nexus5?