Consider provide more info for AU/UA conflict

[bootleq]

The AU (added by us) conflict status may contain unmerged changes on theirs side, but git doesn't get content on :3.
Is it good to provide information that some changes is on theirs side?

Example: checkout bootleq/try-git@3ecc921 (master) and merge bootleq/try-git@2ff6871 ("conflict" branch), and see file Fm.txt.