bug#1122: say how to turn OFF auto-fill with local variables

[jidanni@jidanni.org]

In (info "(emacs)Specifying File Variables")
      For example, you may be tempted to try to turn on Auto Fill mode with
   a local variable list.  That is a mistake.  The choice of Auto Fill mode
   or not is a matter of individual taste, not a matter of the contents of
   particular files.  If you want to use Auto Fill, set up major mode hooks
   with your `.emacs' file to turn it on (when appropriate) for you alone
   (*note Init File::).  Don't use a local variable list to impose your
   taste on everyone.
OK, but say how to (turn it on and OFF, supposing we have it on by
default) anyway with local variables, just in case.