make commands take session names

doc/startify.txt

@@ -106,6 +106,9 @@ There are only two commands for handling sessions:
     :SLoad    load a session
     :SSave    save a session
 
+These take either 0 or 1 argument. If you don't specify the session name as an
+argument, they will just ask for it.
+
 
 ==============================================================================
 5. About the author                                            *startify-author*

plugin/startify.vim

@@ -11,8 +11,8 @@ let g:loaded_startify = 1
 " Init {{{1
 let g:startify_session_dir = resolve(expand(get(g:, 'startify_session_dir', '~/.vim/session')))
 
-command! -nargs=? -bar SSave call startify#save_session(<args>)
-command! -nargs=? -bar SLoad call startify#load_session(<args>)
+command! -nargs=? -bar SSave call startify#save_session(<f-args>)
+command! -nargs=? -bar SLoad call startify#load_session(<f-args>)
 
 augroup startify
   autocmd!