Add swift package reference (#5728)
Add swift package reference (#5728)

Co-authored-by: Peter Jung <7825162b9a986ea992388e58abb7984c7eca9f34@heureka.cz>
dmlc/xgboost,dmlc/xgboost,dmlc/xgboost,dmlc/xgboost,dmlc/xgboost,dmlc/xgboost