replace iris in docs

R-package/man/xgb.cv.Rd

@@ -63,4 +63,10 @@ Number of threads can also be manually specified via "nthread" parameter.
 
 This function only accepts an \code{xgb.DMatrix} object as the input.
 }
+\examples{
+data(agaricus.train, package='xgboost')
+dtrain <- xgb.DMatrix(agaricus.train$data, label = agaricus.train$label)
+history <- xgb.cv(data = dtrain, nround=3, nfold = 5, metrics=list("rmse","auc"),
+                  "max_depth"=3, "eta"=1, "objective"="binary:logistic")
+}