Minor docstring fix.

Thanks to Peter Münster for spotting this.

lisp/org.el

@@ -16101,7 +16101,7 @@ changes from another.  I believe the procedure must be like this:
 ;;;###autoload
 (defun org-switchb (&optional arg)
   "Switch between Org buffers.
-With a prefix argument, restrict available to files.
+With one prefix argument, restrict available buffers to files.
 With two prefix arguments, restrict available buffers to agenda files.
 
 Defaults to `iswitchb' for buffer name completion.