Fix collape_rows for arbitrary columns
diff --git a/man/collapse_rows.Rd b/man/collapse_rows.Rd
index 9508bd4..4752d80 100644
--- a/man/collapse_rows.Rd
+++ b/man/collapse_rows.Rd
@@ -13,7 +13,8 @@
\arguments{
\item{kable_input}{Output of \code{knitr::kable()} with \code{format} specified}
-\item{columns}{Numeric column positions where rows need to be collapsed.}
+\item{columns}{A numeric value or vector indicating in which column(s) rows
+need to be collapsed.}
\item{valign}{Select from "top", "middle"(default), "bottom". The reason why
"top" is not default is that the multirow package on CRAN win-builder is