trivial: Add HighlightJS license for bundled copies
trivial: Add HighlightJS license for bundled copies

The HighlightJS code isn't in the AppStream sources, but we may ship
with the minified JS code when distributing prebuilt documentation.
Therefore, having the license file around is probably better.

ximion/appstream,ximion/appstream,ximion/appstream,ximion/appstream