bug#22240: Build instructions for 64-bit Windows?

[Eli Zaretskii]

> From: Brian Burns <bburns.km@gmail.com>
> Date: Wed, 30 Dec 2015 01:08:38 -0600
> Cc: 22240@debbugs.gnu.org, Chris Zheng <chriszheng99@gmail.com>
> 
> Thanks for the feedback - the updated file is included at the end and at
> https://gist.github.com/bburns/43c9f170361aecee3b71 - Chris added a 
> few comments there. 

Thanks, pushed to the emacs-25 branch.