add note about booster's R parameters

R-package/R/xgb.train.R

@@ -216,6 +216,13 @@
 #' only used in the R interface, only kept when using R's serializers like \link{saveRDS}, and
 #' not anyhow used by functions like \link{predict.xgb.Booster}.
 #'
+#' Be aware that one such R attribute that is automatically added is `params` - this attribute
+#' is assigned from the `params` argument to this function, and is only meant to serve as a
+#' reference for what went into the booster, but is not used in other methods that take a booster
+#' object - so for example, changing the booster's configuration requires calling `xgb.config<-`
+#' or 'xgb.parameters<-', while simply modifying `attributes(model)$params$<...>` will have no
+#' effect elsewhere.
+#'
 #' @seealso
 #' \code{\link{callbacks}},
 #' \code{\link{predict.xgb.Booster}},