Add note about .emacs.d Windows path

At least on my Windows 7 machine, `user-emacs-directory` prints `~/.emacs.d`, which is not really useful, since you also then have to realize that the tilde refers to the roaming appdata directory. I think this way of documenting would perhaps be more immediately useful. For probably almost all other platforms the tilde path will work just fine.
Iirc there is an application data directory on xp

Sent from my iPhone

> On Jun 14, 2014, at 3:57 AM, Bozhidar Batsov <notifications@github.com> wrote:
> 
> In README.md:
> 
> > @@ -131,9 +131,7 @@ ln -s path/to/local/repo ~/.emacs.d
> >  cd ~/.emacs.d
> >  ```
> >  
> > -You'd do well to replace `~/.emacs.d` with the value of
> > -`user-emacs-directory` for your OS. You can check the value by doing
> > -`C-h v user-emacs-directory` inside Emacs.
> > +Note that on Windows, the `.emacs.d` directory is usually located at `C:\Users\your_user_name\AppData\Roaming\.emacs.d`, and you should adjust the command appropriately.
> I'm reasonably sure this path is different on Windows XP.
> 
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