To initialise manifest, make sure that you've added and configured your SSH key/connection to github.com then execute the following commands
repo init -u git@github.com:JARVIS-ROM/android.git -b trepo sync --no-tags --no-clone-bundle --optimized-fetch --prune -cIt will sync the source, you can start compilatio after that. If you need help, check the reference device tree at android_device_xiaomi_sweet