doc: improve explanation for directory with fs.rename()

PR-URL: #27963
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>

doc/api/fs.md

@@ -2898,7 +2898,8 @@ changes:
 
 Asynchronously rename file at `oldPath` to the pathname provided
 as `newPath`. In the case that `newPath` already exists, it will
-be overwritten. No arguments other than a possible exception are
+be overwritten. If there is a directory at `newPath`, an error will
+be raised instead. No arguments other than a possible exception are
 given to the completion callback.
 
 See also: rename(2).