Fixes #10497: Fix Windows 8 and Windows Phone 8 behavior and apply to docs

Per #10497, some things for Windows 8, Windows Phone 8, and Internet Explorer 10 are not what they seem. This pull request fixes a few things up around that:

* Drops the global `@ms-viewport` usage that was causing Windows Phone 8 devices to display scaled down versions of a "desktop site"
* Clarifies the docs in the Browser Support section on the Getting Started page to provide additional context
* Applies the fix to the docs so folks have an example to pull from if need be.

/cc @cvrebert @laurentperez