bug#27639: 25.2; Fix syntax for minor mode enabling in dir locals in manual

[Kaushal Modi]

Hello,

I recently stumbled across this Reddit post[1] where a user is trying to enable a minor mode in .dir-locals.el. But he was doing that by setting the mode name to `t'. 

We generally(?) enable minor modes by doing (mode . MINOR) in .dir-locals.el. 

So I thought of looking up the Emacs manual to check that:

Here's an example of a .dir-locals.el file:

((nil . ((indent-tabs-mode . t)
        (fill-column . 80)))

<snip>

This sets ‘indent-tabs-mode’ and fill-column for any file in the directory tree.

That would lead the readers to think that that's how *any* minor mode can be enabled from .dir-locals.el. 

I think that example should be fixed by using a minor mode example that can be enabled using the (mode . MINOR) syntax.

[1]: https://www.reddit.com/r/emacs/comments/6malb6/disable_warning_message_when_enabling_minor_modes/

--

Kaushal Modi