Add ULiège to ADOPTERS.md.

[gaulthiergain]

Prerequisite checklist

• Read the contribution guidelines regarding submitting new changes to the project;
• Tested your changes against relevant architectures and platforms;
• Ran the checkpatch.uk on your commit series before opening this PR;
• Updated relevant documentation.

Base target

• Architecture(s): N/A
• Platform(s): N/A
• Application(s): N/A

Additional configuration

N/A

Description of changes

Add the University of Liège (ULiège) to ADOPTERS.md (DCO.txt is included).

[razvand]

Thanks, @gaulthiergain.

Reviewed-by: Razvan Deaconescu razvand@unikraft.io
Approved-by: Razvan Deaconescu razvand@unikraft.io