Update documentation for E_loo() function

Clarify the conditions for reliable estimates in E_loo()

Author: avehtari

R/E_loo.R

@@ -5,9 +5,10 @@
 #' [PSIS][psis()] smoothing procedure. The expectations estimated by the
 #' `E_loo()` function assume that the PSIS approximation is working well.
 #' **A small [Pareto k][pareto-k-diagnostic] estimate is necessary,
-#' but not sufficient, for `E_loo()` to give reliable estimates.** Additional
-#' diagnostic checks for gauging the reliability of the estimates are in
-#' development and will be added in a future release.
+#' but not sufficient, for `E_loo()` to give reliable estimates. If 
+#'  If `log_ratios` argument is provided, `E_loo()` computes also a function
+#'  specific Pareto k, which needs also to be small for a reliable estimate. 
+#   See more below.
 #'
 #' @export
 #' @param x A numeric vector or matrix.