Update runtime files.

runtime/doc/vim.1

@@ -416,6 +416,10 @@ Denotes the end of the options.
 Arguments after this will be handled as a file name.
 This can be used to edit a filename that starts with a '\-'.
 .TP
+\-\-clean
+Do not use any personal configuration (vimrc, plugins, etc.).  Useful to see if
+a problem reproduces with a clean Vim setup.
+.TP
 \-\-echo\-wid
 GTK GUI only: Echo the Window ID on stdout.
 .TP