Update config-default.yaml

Typo, add reference

kge/config-default.yaml

@@ -330,7 +330,7 @@ eval:
  # Type of evaluation (entity_ranking only at the moment)
  type: entity_ranking
 
- # How to handle cases ties between the correct answer and other answers, e.g.,
+ # How to handle cases with ties between the correct answer and other answers, e.g.,
  # Query: (s, p, ?).
  # Answers and score: a:10, b:10, c:10, d:11, e:9
  # Correct: 'a'.
@@ -340,8 +340,9 @@ eval:
  # score as the correct answer. In example: 4.
  # - best_rank: Use the lowest rank of all answers that have the same
  # score as the correct answer (competition scoring). In
- # example: 2. DO NOT USE THIS OPTION, it leads to
- # misleading evaluation results.
+ # example: 2. 
+ # DO NOT USE THIS OPTION, it leads to misleading evaluation 
+ # results. See https://arxiv.org/pdf/1911.03903.pdf
  # - rounded_mean_rank: Average between worst and best rank, rounded up
  # (rounded fractional ranking). In example: 3.
  tie_handling: rounded_mean_rank