Your proof package
Your model result is only believable when someone can see how you tested it. Put the evaluation in the repo and in the demo description, not only in your head.
The minimum proof package is: dataset, split method, baseline, confusion matrix, key metric, and one limitation.
Where it goes
Use two places. First, write an Evaluation section in your README or project description. Second, mention the same result in your demo script or video.
If judges are short on time, they should still understand what the model was tested on and what it cannot do yet.